SCIENCE AND HUMAN ORIGINS<\/p>\n
ANN GAUGER<\/p>\n
DOUGLAS AXE<\/p>\n
CASEY LUSKIN<\/p>\n
SEATTLE
\nDISCOVERY INSTITUTE PRESS
\n2012<\/p>\n
Description
\nEvidence for a purely Darwinian account of human origins is supposed to be overwhelming. But is it? In this provocative book, three scientists challenge the claim that undirected natural selection is capable of building a human being, critically assess fossil and genetic evidence that human beings share a common ancestor with apes, and debunk recent claims that the human race could not have started from an original couple.<\/p>\n
Copyright Notice
\nCopyright \u00a9 2012 by Discovery Institute and the respective authors. All Rights Reserved.<\/p>\n
Publisher\u2019s Note
\nThis book is part of a series published by the Center for Science & Culture at Discovery Institute in Seattle. Previous books include The Deniable Darwin by David Berlinski, In the Beginning and Other Essays on Intelligent Design by Granville Sewell, Alfred Russel Wallace: A Rediscovered Life by Michael Flannery, The Myth of Junk DNA by Jonathan Wells, and Signature of Controversy, edited by David Klinghoffer.<\/p>\n
Library Cataloging Data
\nScience and Human Origins by Ann Gauger, Douglas Axe, and Casey Luskin
\nIllustrations by Jonathan Aaron Jones and others as noted.
\n124 pages
\nLibrary of Congress Control Number: 2012934836
\nBISAC: SCI027000 SCIENCE \/ Life Sciences \/ Evolution
\nBISAC: SCI029000 SCIENCE \/ Life Sciences \/ Genetics & Genomics
\nISBN-13: 978-1-936599-04-2 (paperback)<\/p>\n
Publisher Information
\nDiscovery Institute Press, 208 Columbia Street, Seattle, WA 98104
\nInternet: http:\/\/www.discoveryinstitutepress.com\/
\nCover Design: Brian Gage
\nInterior Layout: Michael W. Perry<\/p>\n
CONTENTS<\/p>\n
INTRODUCTION<\/p>\n
1 SCIENCE AND HUMAN ORIGINS<\/p>\n
Ann Gauger<\/p>\n
2 DARWIN\u2019S LITTLE ENGINE THAT COULDN\u2019T<\/p>\n
Douglas Axe<\/p>\n
3 HUMAN ORIGINS AND THE FOSSIL RECORD<\/p>\n
Casey Luskin<\/p>\n
4 FRANCIS COLLINS, JUNK DNA, AND CHROMOSOMAL FUSION<\/p>\n
Casey Luskin<\/p>\n
5 THE SCIENCE OF ADAM AND EVE<\/p>\n
Ann Gauger<\/p>\n
INTRODUCTION<\/p>\n
G. K. CHESTERTON PUT IT WELL IN THE EVERLASTING MAN: \u201cMAN is not merely an evolution but rather a revolution.\u201d
\nChesterton\u2019s comment neatly captures the unease many people have felt about Darwinian explanations of human origins right from the start. Even Alfred Russel Wallace, co-founder with Darwin of the theory of evolution by natural selection, eventually rejected a fully Darwinian explanation of human beings, preferring a form of intelligent design as an alternative.
\nSince Darwin first proposed his theory of unguided evolution more than a century-and-a-half ago, similar doubts have been expressed by a parade of other scientists, philosophers, and public intellectuals.
\nYet in recent years the public has been told\u2014repeatedly\u2014that the case for a purely Darwinian account of human origins is now beyond dispute. Indeed, hardly a month goes by without a new fossil fragment or scientific study being touted as further incontestable proof that the evidence for human evolution is well nigh overwhelming.
\nBut is the evidence for a Darwinian account of human origins really so persuasive?
\nIn this book, three scientists tackle that question. Their findings may surprise you. Ann Gauger is a developmental and molecular biologist with research experience at MIT, the University of Washington, and Harvard University. Douglas Axe is a molecular biologist who has held research scientist positions at Cambridge University, the Cambridge Medical Research Council Centre, and the Babraham Institute in Cambridge. Casey Luskin holds a graduate degree in earth sciences from the University of California at San Diego and has conducted geological research at the Scripps Institute for Oceanography. All three have published work in peer-reviewed science journals. All three have done \u201cbench\u201d science, not just science writing.
\nAnd all three think Darwin\u2019s theory is inadequate to account for both human origins and human uniqueness.
\nBefore going on, it might be helpful to define what is being talked about when this book refers to \u201cDarwinian\u201d evolution. In public discussions today, evolution is a slippery term that can mean anything from generic change over time (an idea no one disputes) to an undirected historical process of \u201csurvival of the fittest\u201d leading from one-celled organisms to man.
\nStrictly speaking, modern Darwinian theory (often called \u201cneo-Darwinism\u201d) has two key planks: common descent and natural selection acting on unplanned genetic variations.
\nCommon descent is the idea that all animals now living have descended from one or a few original ancestors through a process Darwin called \u201cdescent with modification.\u201d According to this idea, not only humans and apes share an ancestor, but so do humans, clams, and fungi.
\nNatural selection is the idea of \u201csurvival of the fittest.\u201d Modern Darwinian theory combines natural selection with the insights of modern genetics: Randomly occurring mutations and recombinations in genes produce unplanned variations among individual organisms in a population. Some of these variations will help organisms survive and reproduce more effectively. Over time, these beneficial variations will come to dominate a population of organisms, and over even more time, these beneficial variations will accumulate, resulting in entirely new biological features and organisms.
\nAs Darwin himself made clear, natural selection is an unintelligent process that is blind to the future. It cannot select new features based on some future goal or potential benefit. As a result, evolution in a Darwinian sense is \u201cthe result of an unguided, unplanned process,\u201d to cite the words of 38 Nobel laureates who issued a statement defending Darwin\u2019s theory in 2005.
\nIn the Darwinian view, amazing biological features such as the vertebrate eye, or the wings of butterflies, or the blood-clotting system, are in no way the purposeful result of evolution. Rather, they are the unintended byproducts of the interplay of chance (random genetic mutations and recombinations) and necessity (natural selection). The same holds true for higher animals such as human beings. In the words of late Harvard paleontologist George Gaylord Simpson: \u201cMan is the result of a purposeless and natural process that did not have him in mind.\u201d
\nThis book is focused on the scientific arguments about human evolution. But it should be obvious there is a larger cultural context to the debate.
\nMany secular Darwinians employ Darwin\u2019s theory as a battering ram to topple the idea of human exceptionalism. According to late Harvard paleontologist Stephen Jay Gould, Darwinian \u201cbiology took away our status as paragons created in the image of God.\u201d Indeed, in the Darwinian view human beings are but \u201ca fortuitous cosmic afterthought.\u201d Princeton University bioethicist Peter Singer expresses a similar view. A champion of infanticide for handicapped human newborns, Singer makes clear that Darwinism supplies the foundation for his debased view of human beings: \u201cAll we are doing is catching up with Darwin. He showed in the 19th century that we are simply animals. Humans had imagined we were a separate part of Creation, that there was some magical line between Us and Them. Darwin\u2019s theory undermined the foundations of that entire Western way of thinking about the place of our species in the universe.\u201d Darwin is likewise a patron saint for many radical environmentalists. In the approving words of former Earth First! activist Christopher Manes, \u201cDarwin invited humanity to face the fact that the observation of nature has revealed not one scrap of evidence that humankind is superior or special, or even particularly more interesting than, say, lichen.\u201d
\nMany religious Darwinists, meanwhile, use Darwinian science to urge revisions in traditional Christian teachings about both God and man. Karl Giberson, a co-founder of the pro-theistic-evolution BioLogos Foundation, argues that human beings were evil from the start because evolution is driven by selfishness; therefore, Christians must abandon the idea that human beings were originally created by God morally good. Current BioLogos president Darrel Falk urges Christians to scrap their outdated belief in Adam and Eve as parents of the human race, claiming that evolutionary biology now proves \u201cthere was never a time when there was a single first couple, two people who were the progenitors of the entire human race.\u201d And geneticist Francis Collins, the original inspiration for BioLogos, puts forward a watered-down view of God\u2019s sovereignty over the natural world. In one part of his book The Language of God, Collins claims (wrongly) that the human genome is riddled with functionless \u201cjunk DNA,\u201d which he claims is evidence against the idea that human beings were specifically designed by God. Elsewhere in his book, Collins states that God \u201ccould\u201d have known and specified the outcomes of evolution; but in that case, Collins believes that God made evolution look like \u201ca random and undirected process,\u201d turning God into a cosmic trickster who creates the world by a process meant to mislead us.
\nBiologist Kenneth Miller, author of Finding Darwin\u2019s God, goes considerably further. Miller explicitly argues that God neither knows nor directs the specific outcomes of evolution\u2014including human beings. In Miller\u2019s view, \u201cmankind\u2019s appearance on this planet was not preordained \u2026 we are here not as the products of an inevitable procession of evolutionary success, but as an afterthought, a minor detail, a happenstance in a history that might just as well have left us out.\u201d According to Miller, God did know that undirected evolution would produce some sort of rational creature eventually, but the creature produced by evolution might have been a \u201ca big-brained dinosaur\u201d or \u201ca mollusk with exceptional mental capabilities\u201d rather than a human being.
\nWhether secular or religious, these champions of modern Darwinian theory all share the same underlying assumption: In their view, science has proven Darwinian evolution beyond a shadow of a doubt; therefore our understanding of human beings and the rest of life must be radically reshaped according to Darwinian tenets.
\nBut what if this assumption turns out to be wrong? What if the unbounded faith placed in Darwinian theory\u2014especially as applied to human beings\u2014is scientifically unwarranted?
\nThe authors of this volume invite you to consider that possibility.<\/p>\n
\u2022 In chapters 1 and 2, Ann Gauger and Douglas Axe challenge the central claim that Darwin\u2019s undirected mechanism of natural selection is really capable of building a human being.<\/p>\n
\u2022 In chapters 1, 3, and 4, Ann Gauger and Casey Luskin critically assess the genetic and fossil evidence that human beings share a common ancestor with apes.<\/p>\n
\u2022 And in the final chapter, Ann Gauger refutes scientific claims that the human race could not have started from an original couple.<\/p>\n
Although much of this book focuses on the shortcomings of Darwinian theory, the scientists represented here are not merely critics of the existing paradigm. Instead, they share a positive vision that much of biology would make better sense from the perspective of intelligent design rather than unguided Darwinian evolution. Often mischaracterized (and wrongly conflated with creationism), intelligent design is simply the effort to investigate empirically whether the exquisitely coordinated features we find throughout nature are the result of an intelligent cause rather than a blind and undirected process like natural selection.
\nBecause intelligent design focuses on whether the development of life was purposeful or blind, it directly challenges the second plank of Darwinian theory (unguided natural selection) rather than the first (common descent). Nevertheless, intelligent design scientists remain free to critically assess the actual evidence for common descent, as they do here.
\nWhether you consider yourself secular, religious, or something in between, the science of human origins raises deep and continuing questions about what it means to be human. You are invited to explore some of these questions in the pages that follow.<\/p>\n
John G. West,Ph.D.
\nAssociate Director, Center for Science and Culture
\nDiscovery Institute, Seattle<\/p>\n
1<\/p>\n
SCIENCE AND HUMAN ORIGINS<\/p>\n
Ann Gauger<\/p>\n
Explaining human origins requires a new way of approaching things. There is no strictly neo-Darwinian path from a chimp-like ancestor to us, no matter how similar we appear to be.<\/p>\n
LATELY THE STORY OF HUMAN ORIGINS HAS BECOME A SUBJECT OF renewed controversy in the media. In 2011 both National Public Radio and Christianity Today ran high-profile stories featuring Christian scholars who claim not only that human beings evolved from ape-like ancestors, but who assert that science has refuted the traditional Christian belief in a first human couple, Adam and Eve. Apparently, these scholars are convinced that the neo-Darwinian account of our origins has now eliminated any need for other explanations. Equally apparently, the media thought this story was newsworthy because the people talking were Christians, who presumably had no bias against religion, and at least some of whom were credible scientists.
\nWhen I first saw these stories, it struck me how uncritically all these people accepted the scientific arguments for human evolution. This is a mistake. Science is not an error-free enterprise, so arguments need to be carefully evaluated. This is especially the case when it comes to a highly charged issue like human evolution.
\nMost of the argument for our common ancestry with ape-like creatures is based on similarity\u2014similarity in anatomy, and similarity in DNA sequence. Yet I know from my own experiments that similarity between two complex structures does not reliably indicate an evolutionary path between them.
\nSimilarity by itself says nothing about what mechanisms are responsible for the apparent relatedness, especially when substantial genetic change is necessary. In fact, there is a surprising disregard among evolutionary biologists for the amount of genetic change that would be needed to actually accomplish the evolutionary transitions they propose, and the amount of time it would require. As I shall explain, these obstacles are a significant factor in human evolution and indicate we cannot have come from an ape-like ancestor by any unguided process.<\/p>\n
WHAT IS THE EVIDENCE FOR COMMON ANCESTRY?<\/p>\n
THE IDEA of our gradual evolution from ape-like ancestors goes all the way back to Darwin himself, although in his time no transitional fossils were known to exist. Since Darwin\u2019s time, paleoanthropologists have uncovered fossil remains that appear to be intermediate in form between great apes and humans. These fossils, together with more recent DNA sequence comparisons from living species, have led to a proposed tree of common descent for the great apes and humans (together referred to as hominids):<\/p>\n
Figure 1-1: Currently accepted tree of common descent for hominids.
\nIllustration: Ann Gauger.<\/p>\n
The ends of the branches represent living genera (groups of species that share similar characteristics), and the branch points represent the last common ancestors from which the genera are thought to have come. The last branch on the tree, assigned the name Hominini, or hominins, includes Pan (chimpanzees), our hypothetical most recent common ancestor with Pan, all the supposed transitional species in between, and us.
\nWhat evidence is there for this tree? As I said previously, it hinges on two kinds of data: anatomical similarities and differences among the great apes, fossil hominins and us; and comparative analysis of DNA sequences from living species. It also depends on one very big but unproven assumption\u2014that any similarities found are due to descent from a common ancestor. It is that assumption I wish to challenge in this chapter.
\nThe fossil evidence for our evolution from apes is actually quite sketchy. Ancient hominin fossils are rare, and they typically consist of bone fragments or partial disarticulated skeletons obtained from different locations around the world and from different geologic strata. They fall into two basic categories: ape-like fossils, and Homo-like fossils. This discontinuity between fossil types is well-known. Nonetheless, the hominin fossils have been interpreted as historical, physical evidence of our common ancestry with apes. Ernst Mayr, a well-known evolutionary biologist, acknowledged both the gap and the story-telling in his book What Makes Biology Unique:<\/p>\n
The earliest fossils of Homo, Homo rudolfensis and Homo erectus, are separated from Australopithecus by a large, unbridged gap. How can we explain this seeming saltation? Not having any fossils that can serve as missing links, we have to fall back on the time-honored method of historical science, the construction of a historical narrative.<\/p>\n
The resulting historical narrative is familiar to us all, as depicted in drawings commonly found in National Geographic and similar magazines.
\nThe evidence from DNA comparisons is similarly enigmatic. DNA sequences are strings of nucleotides millions or billions in length. Aligning DNA sequences in order to compare them is a tricky business. There can be single bases changes, insertions or deletions, duplications, and rearrangements of the DNA that complicate things and may or may not be included in comparisons. The degree of similarity calculated depends on how the analysis is done, and what is excluded or included. But putting aside arguments about how similar we are to chimps, the question is: What does similarity demonstrate?
\nFor most biologists, similarity is assumed to confirm that humans and chimps are linked together by common ancestry. This assumption underlies all evolutionary reasoning. But note that similarity of structure or sequence cannot confirm common descent by itself. \u201cMustang\u201d and \u201cTaurus\u201d cars have strong similarities, too, and you could argue that they evolved from a common ancestor, \u201cFord.\u201d But the similarities between these cars are the result of common design, not common ancestry.
\nFor any story about common ancestry to be verified, including the proposed story of our common ancestry, two things must be shown. First, a step-wise adaptive path must exist from the ancestral form to the new form, whether it is to a new gene, a new protein, or a new species; and second, if it is to have happened by an unguided, neo-Darwinian mechanism, there must be enough time and probabilistic resources for neo-Darwinian processes to traverse that path. The neo-Darwinian mechanisms of mutation, recombination, genetic drift and natural selection must be enough to produce the proposed innovation in the time available. These two things, a step-wise, adaptive path, and enough time and probabilistic resources for the path to be traversed, are absolutely necessary for neo-Darwinian evolution to have occurred.
\nYet these two things have yet to be demonstrated for any significant evolutionary transition. In what follows, I will show that these two things haven\u2019t been demonstrated for human evolution\u2014and probably never will be.<\/p>\n
AN EXPERIMENTAL TEST<\/p>\n
HOW REALISTIC is it for humans to have evolved by neo-Darwinian means? We can\u2019t go back and observe the past directly, so we need to assess the likelihood of much simpler transitions, the kinds of changes that are testable in the lab.
\nProteins that look alike are commonly assumed to have a common evolutionary origin. If the proteins have different functions, then it is assumed that some sort of neo-Darwinian process led to their duplication and divergence. This is the story of common descent writ small. But unlike humans and chimps, proteins can be easily manipulated and tested in the lab for successful functional change. We can actually establish how many mutations are required to switch old proteins to new functions, and thus determine what kinds of innovations are possible according to the rules of neo-Darwinism. If the neo-Darwinian story fails here, it fails everywhere.<\/p>\n
Figure 1-2: Kbl and BioF, two structurally similar proteins from E. coli.
\nIllustration: Ann Gauger and Douglas Axe.<\/p>\n
My colleague Douglas Axe and I took two bacterial proteins that look a great deal alike, but have distinctly different functions. They are thought to be evolutionary cousins, descended from a common ancestor millions of years ago, because of their similar structures. These proteins, called Kbl and BioF, are shown in Figure 1-2 above. Kbl and BioF are not directly descended from the other; nonetheless, a functional shift from something like Kbl to something like BioF must be possible if neo-Darwinism is true. Functional shifts like this one are found everywhere in families of related proteins, and so should be relatively easy to achieve.
\nYet when we experimentally determined how many mutations it would take, we found that it would take at least seven mutations to evolve one enzyme into the other\u2014too many mutations to have occurred by an unguided neo-Darwinian process.
\nBacteria are genetic workhorses for evolutionary research, precisely because they are capable of rapid adaptation\u2014as long as it takes only one or two mutations. Three coordinated mutations are a stretch even for bacteria, if all of the intermediates are neutral (have no beneficial effect for the organism). But for one of our enzymes to evolve the other\u2019s function, it would take at least seven and probably many more mutations. The waiting time for seven coordinated neutral mutations to arise in a bacterial population is on the order of 1027 years. To put that in some sort of perspective, remember that the universe is only about 1010 years old. It can\u2019t have happened.
\nYet this is precisely the kind of transition that neo-Darwinism is meant to explain\u2014structurally similar, yet functionally distinct proteins should be able to diverge by a process of mutation and selection. If this shift in function is not within reach of known neo-Darwinian mechanisms, something else must be going on.
\nIn case you are wondering, our result is in line with other published research on recruitment of proteins to new functions. Attempts to convert proteins to genuinely new functions typically require eight or more mutations, well beyond the reach of neo-Darwinian processes.<\/p>\n
GETTING TO HUMAN<\/p>\n
THE RESEARCH I described above has shown that similarity of structure is not enough to establish that there is an adaptive path between two proteins with distinct functions. In fact, it is likely to be the case that, in general, neo-Darwinian processes are not sufficient to produce genuine innovations, because too many specific mutations are required. Now we need to consider whether or not this analysis also applies to the necessary transitions to get from an ape-like ancestor to us.
\nLet\u2019s begin by considering what distinguishes us from great apes. What are our distinctive characteristics? There are significant anatomical differences, of course: Our upright walking, longer legs and shorter arms, changes in muscle strength, our significantly larger brains and skulls (three times bigger than great apes), and our refined musculature in hands, lips and tongues. There are also our relative hairlessness and changes to our eyes. More importantly, there are whole realms of intellect and experience that make us unique as humans. Abstract thought, art, music, and language: These things separate us from lower animals fundamentally, not just in degree but in kind.
\nHow many mutations might be required to produce these kinds of innovations? We really have very little data by which to track intellectual changes, so let\u2019s consider just the physical characteristics that distinguish us from chimps.
\nChimps are suited for life in the trees. Humans are suited for life on the ground, walking and running. The anatomical changes needed to move from tree-dwelling to complete terrestrial life are many. To walk and run effectively requires a new spine, a different shape and tilt to the pelvis, and legs that angle in from the hips, so we can keep our feet underneath us and avoid swaying from side to side as we move. We need knees, feet and toes designed for upright walking, and a skull that sits on top of the spine in a balanced position. (The dome of our skull is shifted rearward in order to accommodate our larger brain and yet remain balanced.) Our jaws and muscle attachments must be shifted, our face flattened, and the sinuses behind the face and the eye sockets located in different places, to permit a forward gaze and still be able to see where to put our feet.<\/p>\n
Figure 1-3: Comparison of hominin anatomy. Human [(a) and (c)] and chimp [(b) and (d)] skeletons and major muscles involved in running are shown. H. erectus (e) and A. afarensis (f) are drawn to the same scale, with the existing bones for each shown in black. White bones in (e) and (f) are hypothetical.
\nIllustration: Adapted by Jonathan Jones with permission from Macmillan Publishers Ltd: Nature, Dennis M. Bramble and Daniel E. Lieberman, \u201cEndurance running and the evolution of Homo,\u201d 432 (2004): 345\u2013352, Figure 3, copyright 2004.<\/p>\n
Many of these differences can be seen in Figure 1-3 above. Humans (a,c), and chimps (b,d), have significantly different shoulders, rib cages, spines, pelvises, hips, legs, arms, hands and feet, each appropriate for different modes of living.
\nNow let\u2019s consider the proposed evolutionary story based on the fossil record. Shown next to the chimp and human figures are two hominin figures, Homo erectus (e), and Austalopithicus afarensus (f), reconstructed from the partial skeletal remains of \u201cTurkana boy\u201d from 1.6 million years ago (mya) and \u201cLucy\u201d (3.2 mya), respectively. In this drawing \u201cLucy\u201d resembles a chimp in most respects, though her leg and pelvis bones suggest she spent time walking upright. Scientists debate the degree to which her lifestyle was terrestrial, however, as certain elements of her frame would have made walking inefficient.
\n\u201cTurkana boy,\u201d in contrast, is much more similar in anatomy to modern humans. His hominin species, Homo erectus, first appeared in the fossil record about two mya ago, with all the adaptations in place for fully upright travel, including running over long distances. His only obvious difference from Homo sapiens is his skull, which though substantially larger than that of A. afarensis, is smaller than that of modern humans (though not outside the range of modern human genetic variation).
\nIf our common ancestry with chimps is true, the transition to fully human must include something like the shift from A. afarensis to H. erectus. And here is where the discontinuity lies. H. erectus is the first fossil species with a nearly modern human anatomy and a constellation of traits not seen in any prior hominin. There simply is no good transitional species to bridge the gap. As John Hawks, a paleoanthropologist at the University of Wisconsin\/Madison states:<\/p>\n
No australopithecine species is obviously transitional [to Homo erectus].\u2026 Our interpretation is that the changes are sudden and interrelated and reflect a bottleneck that was created because of the isolation of a small group from a parent australopithecine species. In this small population, a combination of drift and selection resulted in a radical transformation of allele frequencies, fundamentally shifting the adaptive complex; in other words, a genetic revolution. [Emphasis added, internal citations removed for clarity.]<\/p>\n
SO MUCH TO DO, SO LITTLE TIME<\/p>\n
FOR THE purposes of my argument, I don\u2019t intend to argue that H. erectus was or was not the first human being, or is directly part of our lineage. Instead, I want to focus on the anatomical changes that must be accomplished to go from A. afarensis to H. erectus. Regardless of whether or not other transitional hominins are found, these are the kinds of anatomical changes that must have occurred.
\nFor a \u201cradical transformation\u201d of this kind to have happened by strictly neo-Darwinian means, as Hawks et al. imply, then some combination of mutation, genetic drift, and natural selection must be capable of producing the change. But \u201cshifting the adaptive complex\u201d to the new H. erectus anatomy would require reorganizing multiple anatomical structures, the kind of thing likely to require multiple specific mutations.
\nTwo questions then arise: (1) How many mutations would it take to turn an australopithecine species into a Homo erectus? And (2) If there are only one and a half million years between A. afarensis and H. erectus, can neo-Darwinism produce the necessary changes in the time allotted?
\nHow many mutations would it take? Bramble and Lieberman count sixteen features of the human body that first appear in H. erectus or H. sapiens. These features are necessary to stabilize the head, permit counter-rotation of the torso with the head and hips, stabilize the trunk, absorb shock and transfer energy during running. Many of these changes must occur together to be of any benefit.
\nIs there enough time to get sixteen anatomical changes by a neo-Darwinian process? Each of these new features probably required multiple mutations. Getting a feature that requires six neutral mutations is the limit of what bacteria can produce. For primates (e.g., monkeys, apes and humans) the limit is much more severe. Because of much smaller effective population sizes (an estimated ten thousand for humans instead of a billion for bacteria) and longer generation times (fifteen to twenty years per generation for humans vs. a thousand generations per year for bacteria), it would take a very long time for even a single beneficial mutation to appear and become fixed in a human population.
\nYou don\u2019t have to take my word for it. In 2007, Durrett and Schmidt estimated in the journal Genetics that for a single mutation to occur in a nucleotide-binding site and be fixed in a primate lineage would require a waiting time of six million years. The same authors later estimated it would take 216 million years for the binding site to acquire two mutations, if the first mutation was neutral in its effect.<\/p>\n
FACING FACTS<\/p>\n
BUT SIX million years is the entire time allotted for the transition from our last common ancestor with chimps to us according to the standard evolutionary timescale. Two hundred and sixteen million years takes us back to the Triassic, when the very first mammals appeared. One or two mutations simply aren\u2019t sufficient to produce the necessary changes\u2014sixteen anatomical features\u2014in the time available. At most, a new binding site might affect the regulation of one or two genes. Durrett and Schmidt acknowledge the problem, and suggest that it can be overcome because there are an estimated 20,000 genes evolving independently, many of which might benefit from mutation(s) in their regulatory regions.
\nThis is unreasonable. Having 20,000 genes available for change does not make the task easier. Many of the anatomical changes seen in H. erectus had to occur together to be of benefit. Individually they would be useless or even harmful. So even if a random mutation or two resulted in one change, they would be unlikely to be preserved. And getting all sixteen to appear and then become fixed within six million years, let alone the one and a half million that it apparently took, can\u2019t have happened through an unguided process.
\nTo get an idea of why it won\u2019t work, imagine letting your toddler loose on your computer operating system, allowing her to randomly change 1s to 0s, or insert or delete stretches of 1s and 0s, or rearrange them in the code. How likely is it that she will develop a new subroutine that improves the function of the operating system? Unless you had the foresight to write an executive program that wipes out all changes that reduce the efficiency of the operating system or crash it, she will crash the system. Even with an executive program that eliminates crash-inducing changes and rewards efficiency, her haphazard changes are very unlikely to ever create a new subroutine. This is because the executive function has no foresight and can\u2019t see that certain changes, if preserved, may lead eventually to a valuable new subroutine.
\nThat toddler is like mutation, and natural selection is like that executive function. Natural selection may be good at weeding out mistakes that make the system crash or reduce efficiency, but it\u2019s really bad at innovation. It has no foresight, and can\u2019t predict which changes could lead to an innovation and then preserve them. It lacks intention. In fact, natural selection often permits the loss of considerable functional genetic information if it gives some slight survival advantage in the current environment.
\nRemember, any innovation that requires more than six specific neutral changes is impossible for bacteria, even with their rapid growth rates and large population sizes. For large mammals like us, the picture for neo-Darwinism is much, much bleaker.
\nHow many mutations would it take to evolve the anatomical changes necessary for walking and running? Dozens if not hundreds or thousands\u2014if it could happen by random mutation at all. If the time span available for human evolution from a chimp-like ancestor is six million years, the effective population size is ten thousand, the mutation rate is 10\u22128 per nucleotide per generation and the generation time is five to ten years (for a chimp-like ancestor), only a single change to a particular DNA binding site could be expected to arise. It strains credibility to think that all sixteen anatomical features evolved fortuitously in that same time frame, especially if each required multiple mutations. Given these numbers, it is extremely improbable, if not absolutely impossible, for us to have evolved from hominin ancestors by a gradual, unguided process.<\/p>\n
HUMAN EXCEPTIONALISM<\/p>\n
THE ABOVE argument was based solely on the anatomical changes required for fully upright, bipedal posture and efficient long-distance travel. But I cannot leave this discussion without pointing out the many other things that distinguish us from apes. At the fine motor level, we have many abilities that require anatomical features that apes lack\u2014we have many more finely controlled muscles in our hands, face, and tongues, for example. Without them our dexterity as artists or craftsmen, our ability to converse, and our ability to express fine distinctions in emotion by our facial expressions would be impossible.
\nBut even more significant are our cognitive and communicative abilities. We are much more than upright apes with fine motor control. Our capacity for abstract thought, self-conscious reflection, and ability to communicate put us in another category entirely. These attributes are orders of magnitude more complex than anything animals can do. For example, language requires both anatomical features (the position of our larynx and language centers in our brains), and a mysterious innate knowledge of the rules of grammar that appears to be hard-wired into our brain. Three-year-olds know these rules instinctively. Apes don\u2019t. True language requires the ability to think abstractly. Words are symbols that stand in for things and ideas. We communicate by arranging words into complex symbolic utterances. We think new thoughts and convey new ideas to others. We reflect on ourselves. We discuss our origins, write sonnets, and describe both imaginary worlds and the real one we inhabit. Language both reflects and enriches our capacity for abstract thinking and creativity.
\nWhere did these massive increases in fine-motor dexterity, and the quantum leaps of language, art, and abstract thought come from? Our uniquely human attributes constitute a quantum leap, not just an innovation, a leap that cannot have arisen without guidance. We are not souped-up apes.
\nExplaining our origin requires a new way of approaching things. There is no strictly neo-Darwinian path from a chimp-like ancestor to us, no matter how similar we appear to be. The mechanisms of random mutation, natural selection and genetic drift are insufficient to accomplish the needed changes in the time allotted, so other explanations need to be explored. Are we the product of some sort of necessary cosmic unfolding? The lucky result of an ever-ramifying series of universes? Or are we the embodiment of intelligent design by an agent or agents unknown?
\nWhen evaluating explanatory causes for beings such as ourselves, we need to choose a cause that is up to the task. I personally am convinced that unguided, unintelligent processes can\u2019t do the job, not only because the neo-Darwinian mechanism is utterly insufficient, but also because we are beings capable of intelligence and creativity. These qualities are what make us human, and together with our capacity for empathy and our desire for goodness and beauty, they point toward the kind of cause that is sufficient to explain our origins.<\/p>\n
Figure 1-4 Humans are exceptional in their creativity, their artistry, and their exercise of reason.
\nIllustration: Annbale Caracci, \u201cStudio di nudo maschile,\u201d public domain, reprinted from Wikimedia Commons.<\/p>\n
2<\/p>\n
DARWIN\u2019S LITTLE ENGINE THAT COULDN\u2019T<\/p>\n
Douglas Axe<\/p>\n
When it comes to producing major innovations in the history of life like human beings, Darwin\u2019s engine of natural selection acting on random variations has proved to be the little engine that couldn\u2019t\u2014certainly not in the time allowed by most scientists, and probably not even in trillions of years.<\/p>\n
BIOLOGIST RICHARD DAWKINS, A VOCAL ATHEIST, ONCE DESCRIBED biology as \u201cthe study of complicated things that give the appearance of having been designed for a purpose.\u201d According to him, that appearance is entirely deceptive. Life needed no personal inventor because there is an impersonal one powerful enough to do the job, namely \u201c[n]atural selection, the blind, unconscious, automatic process which Darwin discovered, and which we now know is the explanation for the existence and apparently purposeful form of all life,\u201d including us.
\nThe evidence has convinced me otherwise. This engine of invention that Darwin imagined and Dawkins has spent much of his life promoting doesn\u2019t actually work very well when you put it to the test. I know this because I\u2019ve been doing just that for a number of years, along with several of my colleagues. The results of our work have been described in technical detail. In fact, recognizing that the level of detail in these descriptions is far beyond what non-scientists are looking for, I\u2019m going to focus here on the bigger picture that most interests us, and which has the added advantage of being amenable to communication in ordinary English.
\nThe question of how we humans came to be\u2014living, breathing things capable of pondering our own existence\u2014is deeply connected to how we should think of ourselves. This places it among the most important subjects of human inquiry throughout the ages. Everyone perceives this, but when it comes to evaluating the science that gets drawn on to make arguments on this important topic, most people find themselves in the difficult position of having to judge a debate without speaking the language of the debaters. To add to the difficulty, the debaters themselves can be so emphatic and dogmatic that it seems as though something other than scientific data must be animating the exchange.
\nThe good news is that the situation is not as hopeless as it might look. If careful observation and reasoning have anything decisive to say about our origin, then science provides a way forward. And by that I mean not any particular scientific authority or organization or committee or publication, but rather science itself. Science has always progressed by the conflict of ideas, and whatever benefit some of those ideas have received from things other than the twin pillars of observation and reasoning, those pillars alone will remain standing in the end. Every conclusion they don\u2019t support will fall \u2026 eventually.
\nWith that in mind, my purpose here is to present a key part of the scientific case against Darwinism in terms that everyone can follow, and to tie that case to the great question of our own origin as humans. The best arguments are simple, so the very exercise of distilling an argument to its essence is, in my opinion, the best way for someone who labors over the technical details to step back and see whether anything good has come of it. I believe it has\u2014that careful science now stands decisively against Darwinism. But whether you\u2019re inclined to agree or disagree, my aim is to equip you to decide for yourself.<\/p>\n
DARWIN\u2019S LITTLE ENGINE<\/p>\n
MY COLLEAGUE Ann Gauger and I have recently challenged Darwin\u2019s engine to invent something so much simpler than humanity that the comparison may seem rather odd, and yet there is an important connection between what we examined and human origins. The technical details of our study are available for those who may want to examine them, but all you need to know to follow what I\u2019ll say here is that each gene inside a cell carries the instructions for building a particular protein, and each protein is a tiny machine-like device that carries out one of the many tasks that must be accomplished for the cell to function properly.<\/p>\n
Figure 2-1. A modest test that Darwin\u2019s engine failed. The object on the left is a depiction of the protein that we started with, and the object on the right is a protein that performs the desired new function. Keep in mind that we weren\u2019t asking whether the thing on the left can evolve the precise appearance of the thing on the right. We were simply asking whether it can evolve the function of the thing on the right. That should be possible with only a partial shift in the appearance, which ought to be relatively easy in view of the close resemblance.
\nIllustration: Douglas Axe.<\/p>\n
In those simple terms, all we did was ask whether Darwin\u2019s engine can alter a single gene in bacterial cells so that its instructions specify a modified version of the original protein that performs a new task. We wanted this to work, so we bent over backwards to choose a pair of tasks that ought to make this conversion relatively easy. Since no one can predict how hard it might be to produce a protein function that\u2019s never been seen before, we did a thorough study of known proteins and chose a pair that are very similar but specialize in different tasks (the tasks themselves being similar in kind, but different in detail). In terms of more familiar objects, you can think of our test as being like taking a putter from the golf bag and asking something\u2014some process\u2014to reshape it to work as a pitching wedge. This is a real change of function, but not the fantastical kind that would be needed to get the wedge from a completely different object, like a corkscrew or a halogen lamp. Well, if the process in this example involves a talented metal worker then success is virtually guaranteed. But can something as simple and clueless as Darwin\u2019s engine really do anything comparable?
\nApparently not, according to the results of our experiment. Darwin\u2019s engine proved to be the little engine that couldn\u2019t \u2026 certainly not in the few billion years in which it is supposed to have done everything, and probably not even in a few trillion years.
\nSo, what does this have to do with our own origin? The answer is that it places an important limitation on what we can infer from similarity. Specifically, we now know that we can\u2019t infer that Darwin\u2019s engine can produce thing B from thing A simply because A and B are quite similar. We know this because we have now shown for a particular thing A and a similar thing B that his engine can\u2019t accomplish the transformation (not directly, anyway\u2014more on that below). We also know in broad terms which aspect of our challenge caused the difficulty. It was that we required Darwin\u2019s engine to produce a new function. If we had been content for it to do something less, like modify the starting gene while preserving the function of its specified protein, then it would have passed. But that\u2019s like saying the loser of a contest would be thought a winner if we disregarded the contest. The failure of Darwin\u2019s engine in this case is its downfall precisely because we asked it to prove its most highly touted credentials\u2014its credentials as an inventor.
\nIt will be helpful to summarize our result in the form of a principle as follows:<\/p>\n
Darwinian transitions from A to B that accomplish
\ninvention cannot be presumed plausible simply because A
\nand B are substantially similar.<\/p>\n
If principles can seem presumptuous when first introduced, the modesty of this one surely qualifies it as an exception. It doesn\u2019t say that all Darwinian transitions are implausible, like the one we studied. It simply says that their plausibility can\u2019t be counted on just because they end with something similar to what they started with.
\nSimple though it is, this principle turns out to have enormous implications for Darwinism. To fully grasp them, you have understand how central the concept of similarity has become to evolutionary reasoning. Since evolutionary biologists assume that Darwin\u2019s engine is capable of inventing everything that has been invented in the living world, their interest lies in the historical particulars of the engine\u2019s activity. They want to place life\u2019s key historical events on Darwin\u2019s tree of life, the great family tree he conceived as showing how all species descended from the first life. The general mechanism of invention itself no longer merits attention, this supposedly having been fully explained way back in the first half of the twentieth century when Darwin\u2019s theory was updated with the then current understanding of genetics. All that remains for today\u2019s evolutionary biologists is the business of inferring the details of the great family tree, and for this they need only continue the pursuit of methods for detecting the increasingly faint similarities left behind by increasingly distant familial relationships.
\nThe logic of inference from similarity is very simple: the greater the degree of similarity between two species, the closer their evolutionary relationship. But notice what gets swept away by that simplicity. Having assumed that Darwin\u2019s engine can invent everything that got invented, biologists don\u2019t worry about whether the branches they propose in their attempts to reconstruct parts of the great tree are really plausible or not. The focus is entirely on whether similarities have been detected and grouped in a way that would convince other biologists, the thinking being that if those things are properly documented, then the evolutionary relationships inferred from them must be correct.
\nThat turns out to be precarious reasoning. Considering that Darwin\u2019s engine operates through the ordinary process of procreation, if it really was the great inventor then all species are related in that ordinary procreative sense. But if we have reason to think it wasn\u2019t the great inventor, then the sense in which one species is related to the next must remain an open question until we settle the matter of the fundamental nature of the inventive process. As things now stand, our finding that a particular evolutionary transition between two very similar things is beyond the reach of Darwin\u2019s engine severely undermines the logic of similarity that has underwritten the entire Darwinian tree project. And now that that has been called into question, everything based on it needs to be reexamined.
\nA mental picture may help to clarify what went wrong. Darwinian evolution is often thought of in terms of journeys over a vast rugged landscape. Each point on this strange terrain represents a possible genome sequence, those possibilities being so staggeringly numerous that real organisms have only actualized a minute fraction of them. The ground elevation at each point corresponds to the fitness of individuals carrying that genome, with the horizontal distance between any two points indicating the degree to which the corresponding genomes differ. In terms of this picture, all of the millions of species alive today are represented by their own points, high up on peaks scattered somewhere across this conceptual landscape (the fact that they are alive demonstrates the quality of their genomes).
\nNow, wherever a species happens to be, Darwin\u2019s engine tends to move it toward the highest ground it can reach (Figure 2-2). According to the Darwinian story, that simple tendency to migrate upward has, over billions of years, transported the first primitive genome from its starting point to higher points along millions of diverging paths. The result is the spectacular variety of life forms we see today with a correspondingly wide dispersal of genomes across the vast conceptual landscape.<\/p>\n
Figure 2-2. Darwin\u2019s explanation of the diversity of life forms. This is a cross-section through two peaks representing substantially different forms of life. The whole landscape stretches out in all directions, with millions of peaks representing all the different species. This simple hill-climbing mechanism, repeated million of times, is Darwin\u2019s explanation for the full variety of life.
\nIllustration: Douglas Axe.<\/p>\n
But there\u2019s something suspicious about this story, as a number of careful observers pointed out long before Dr. Gauger and I did our experiment. It has to do with the wide disparity of distance scales. The scale of the landscape, which is characterized by the extent to which dissimilar genomes differ, is very large by any reasonable calculation. On the other hand, Darwin\u2019s engine moves in steps that can only reach points a tiny distance away from the prior point. In one step it can move a genome to the highest point within this reach, but further progress would require a still higher point to fall within reach once that move is made. That might happen every now and then, but it would have to happen in an amazingly consistent and helpful way to explain how the enormous distances were traversed from the point marking the first primitive organism to the millions of points marking the great variety of modern life forms.<\/p>\n
Figure 2-3. The problem of climbing in tiny steps. If the engine moves to the highest point that can be reached in each step and the landscape is rugged, then the endpoint will be a local peak.
\nIllustration: Douglas Axe.<\/p>\n
Let\u2019s put this in more familiar terms. The summit of Mount Whitney, the highest point in the contiguous United States, is just 136 kilometers from the lowest point in North America, known as Badwater Basin. Now, suppose there were an automated vehicle capable of remotely scanning the surrounding terrain within some fixed distance and then moving to the highest point identified by the scan. If the scan radius is greater than 136 kilometers, this vehicle could get from Badwater to Whitney in one scan-and-move operation. But what if the scan radius is one millionth that size? Now the circle that the vehicle \u2018sees\u2019 from its current position is about a shoe-length across, with each move being up to half that distance. Considering how uneven the ground is, we wouldn\u2019t expect this nearsighted vehicle to complete more than a few scan-and-move operations before becoming stuck on a rock, maybe half a pace from where it started. Summiting Whitney would be completely out of the question. So the idea that any ability to seek higher ground, no matter how restricted, makes the highest summit accessible turns out to be highly simplistic.
\nThe very same critique applies to Darwinism. Consider that for Darwin\u2019s engine to invent humans from apes, it would have had to work within the severe limitation of a single-mutation scan radius. That is, it would have had to invent humans one simple mutation at a time, with each of these mutations making its possessors significantly more fit than their peers. Contrast this single-mutation reach with the millions of differences that distinguish the chimp and human genomes and we\u2019re back to the impossible trek from Badwater to Whitney. Maybe the genomic landscape is so much simpler and smoother than the Death Valley terrain as to enable Darwin\u2019s engine to cruise upward to exotic destinations on gentle inclines, but why would anyone assume this to be so? Only if experiment after experiment were to prove that remarkable kind of terrain to be the rule should anyone begin to think that something so fantastic might be true.
\nAlas, the experiment that we performed is one of many that have examined precisely this point, and the clear consensus is that the landscape is anything but smooth and gentle. We focused specifically on invention because this is where smoothness is crucial to the success of Darwin\u2019s evolutionary mechanism. In terms of the landscape picture, we placed Darwin\u2019s engine at a natural location (a genome with the gene for protein A) known to have a natural high peak that is very close to it (the same genome but with a gene for protein B instead). If that close peak had gently sloped faces, then the engine would have climbed it (as in Figure 2-2, but on a much smaller scale). It didn\u2019t. And while there are many examples in the scientific literature where the engine does climb for several steps, we have not found any where a new function was generated in the process. In fact, Darwin\u2019s engine often moves away from invention in its shortsighted pursuit of immediate fitness gains.
\nExperiments will continue to add to this picture, of course. Darwin\u2019s engine can\u2019t drive the short distance from A to B in our test case, but perhaps an even smaller test will be found, and perhaps the engine will pass that test. For that matter, maybe a new protein will eventually be found that sits between our A and B, enabling the engine to traverse paths that connect A and B through that middle point. The important thing to realize, though, is that this wouldn\u2019t remove the problem of the disparity of scales. It is now clear that Darwin\u2019s engine can\u2019t climb a peak corresponding to a new invention unless that peak happens to be remarkably close to its current location\u2014closer than the peak-to-peak distance between any pair of proteins that we know of with distinct functions. Even if such an extraordinary case were to be found, it would be just that\u2014an extraordinary case. Traversing long distances would still depend on a very long and well coordinated succession of extraordinary cases, which amounts to nothing short of a miracle.
\nIn fact, in my effort to simplify I\u2019ve downplayed how extraordinary this would be. Darwin\u2019s engine actually received much more sympathetic treatment in our experiment than it would in nature. Most significantly, we made highly unrealistic arrangements in order for the intended conversion from A to B to be of any use to the bacterial cells we were working with. The truth is that several other conversions would have to occur and the whole set would have to come together by accident in one cell before anything of biological significance would happen. In terms of the landscape picture, that means the nearby peak we challenged Darwin\u2019s engine to climb would actually be much more distant in any realistic scenario.<\/p>\n
THE VIEW FROM SAPIENS SUMMIT<\/p>\n
WHEN IT comes to human origins, all I would add is that the inadequacy of Darwin\u2019s engine must surely become even more profound as the inventions attributed to it become more profound. Of the millions upon millions of amazing examples of invention to be seen among and within living things, none compares to the invention humanity\u2014the invention of inventors. If the show on earth was spectacular when the likes of fireflies and geckos and orcas made their successive entrances, it became something incomparably deeper when humans took their place. Crickets brought more crickets, and chimps more chimps. All very good. Humans, on the other hand, brought the products of their own contemplation: music and drama and literature and painting and sculpture and philosophy and theology and mathematics and science and technology and athletics and culture and movements and politics and war. The best of good mixed with the worst of bad, all of it categorically unlike what came before\u2014the chirping of crickets and the screeching of chimps.
\nSo, if this humanity thing is on a level of its own, how reasonable do you suppose it is to chalk it up to Darwin\u2019s little engine? It\u2019s one thing to say that chimps and humans are similar enough that their likeness calls for careful explanation (few would argue with that), but as we\u2019ve now seen it\u2019s quite another to say that they are similar enough for Darwin\u2019s engine to have traversed the gap between them. To insist on that is to ignore the evidence. A comparison of the complete human and chimp genomes has identified twenty distinct gene families, each with multiple genes, that are present in humans but absent from chimps and other mammals. That\u2019s a huge gap when you compare it to the single in-family gene transition that we examined.
\nThe truth is that humans have a tendency to accept what they\u2019ve been told over and over, and scientists (being human) are no exception to this. Stories have their place in science, in the framing of ideas, but they aren\u2019t what makes good science so persuasive. So, scientists who insist that Darwin got our story, the human story, right would do well to ponder the evidence that would be needed to make that claim persuasive.
\nHave they thought seriously about what an ape-to-human transition would entail? Have they figured out how to wire a brain for speech, or for the intelligence needed to make use of speech? Do they know how to configure the lips, the tongue, and the vocal tract in order for speech to be physically possible? Have they discovered how to coordinate these inventions with all the changes needed for females to give birth to big-brained offspring?
\nAnd if they\u2019ve mastered all these points while wearing their bioengineers\u2019 hats, have they switched to their geneticists\u2019 hats and identified a series of single mutations that would orchestrate this whole inventive process? They may think they know some of the answers to these problems, and that\u2019s a start, but have they gone into the primate lab and done the work that should convince those of us who wonder whether they have it right? Have they been hard at work for decades, quietly validating their ideas by producing talking chimps?
\nIf so, have they done the experiments to measure the fitness effect of each single mutation along the line of chimps that eventually produced the ones that talk? Did they verify that each increases the fitness enough to become established in a natural population? And assuming they have checked all the boxes to this point, did they do the math to verify that the whole transition can happen naturally in an ape population within a few hundred thousand generations?
\nHard questions are humbling, and humility may be the best way for scientists to earn the trust of their benefactors (the public) on this subject. In truth, almost nothing on the above checklist is technically feasible at present, so we don\u2019t need to lose any sleep over the ethical issues. My point is simply that virtually everything that would need to be done to establish the sheer physical possibility of turning apes into humans remains undone. And even in a strange sci-fi thought experiment where it has been done, the knowledge so gained would only further confirm how naive it is to think that Darwin\u2019s little engine could have done it.
\nA closing thought. As someone who loves science, I have to say that I can think of no conclusion in the whole history of the discipline that is so firm and so profound and so original that it should cause every human being to stop and rethink what it means to be human. Most simply aren\u2019t that profound. I happen to think that Darwin\u2019s was that profound, but thankfully, also profoundly wrong.<\/p>\n
3<\/p>\n
HUMAN ORIGINS AND THE FOSSIL RECORD<\/p>\n
Casey Luskin<\/p>\n
Hominin fossils generally fall into one of two groups: ape-like species and human-like species, with a large, unbridged gap between them. Despite the hype promoted by many evolutionary paleoanthropologists, the fragmented hominin fossil record does not document the evolution of humans from ape-like precursors.<\/p>\n
EVOLUTIONARY SCIENTISTS COMMONLY TELL THE PUBLIC THAT THE fossil evidence for the Darwinian evolution of humans from ape-like creatures is incontrovertible. For example, anthropology professor Ronald Wetherington testified before the Texas State Board of Education in 2009 that human evolution has \u201carguably the most complete sequence of fossil succession of any mammal in the world. No gaps. No lack of transitional fossils \u2026 So when people talk about the lack of transitional fossils or gaps in the fossil record, it absolutely is not true. And it is not true specifically for our own species.\u201d According to Wetherington, the field of human origins provides \u201ca nice clean example of what Darwin thought was a gradualistic evolutionary change.\u201d
\nDigging into the technical literature, however, reveals a story starkly different from the one presented by Wetherington and other evolutionists engaging in public debates. As this chapter will show, the fossil evidence for human evolution remains fragmentary, hard to decipher, and hotly debated.
\nIndeed, far from supplying \u201ca nice clean example\u201d of \u201cgradualistic evolutionary change,\u201d the record reveals a dramatic discontinuity between ape-like and human-like fossils. Human-like fossils appear abruptly in the record, without clear evolutionary precursors, making the case for human evolution based on fossils highly speculative.<\/p>\n
THE CHALLENGES OF PALEOANTHROPOLOGY<\/p>\n
HUMANS, CHIMPS, and all of the organisms leading back to their supposed most recent common ancestor are classified by evolutionary scientists as \u201chominins.\u201d The discipline of paleoanthropology is devoted to the study of the fossil remains of ancient hominins. Paleoanthropologists face a number of daunting challenges in their quest to reconstruct a story of hominim evolution.
\nFirst, hominin fossils tend to be few and far between. It\u2019s not uncommon for long periods of time to exist for which there are few fossils documenting the evolution that was supposedly taking place. As paleoanthropologists Donald Johanson (the discoverer of Lucy) and Blake Edgar observed in 1996, \u201c[a]bout half the time span in the last three million years remains undocumented by any human fossils\u201d and \u201c[f]rom the earliest period of hominid evolution, more than 4 million years ago, only a handful of largely undiagnostic fossils have been found.\u201d So \u201cfragmentary\u201d and \u201cdisconnected\u201d is the data that in the judgment of Harvard zoologist Richard Lewontin, \u201cno fossil hominid species can be established as our direct ancestor.\u201d
\nThe second challenge faced by paleoanthropologists is the fossil specimens themselves. Typical hominin fossils consist literally of mere bone fragments, making it difficult to make definitive conclusions about the morphology, behavior, and relationships of many specimens. As the late paleontologist Stephen Jay Gould noted, \u201c[m]ost hominid fossils, even though they serve as a basis for endless speculation and elaborate storytelling, are fragments of jaws and scraps of skulls.\u201d
\nA third challenge is accurately reconstructing the behavior, intelligence, or internal morphology of extinct organisms. Using an example from living primates, primatologist Frans de Waal observes that the skeleton of the common chimpanzee is nearly identical to its sister species, the bonobo, but they have great differences in behavior. \u201cOn the sole basis of a few bones and skulls,\u201d writes de Waal, \u201cno one would have dared to propose the dramatic behavioral differences recognized today between the bonobo and the chimpanzee.\u201d He argues this should serve as \u201ca warning for paleontologists who are reconstructing social life from fossilized remnants of long-extinct species.\u201d De Waal\u2019s example pertains to a case where the investigators have complete skeletons, but the late University of Chicago anatomist C. E. Oxnard explained how these problems are intensified when bones are missing: \u201cA series of associated foot bones from Olduvai [a locality bearing australopithecine fossils] has been reconstructed into a form closely resembling the human foot today although a similarly incomplete foot of a chimpanzee may also be reconstructed in such a manner.\u201d
\nFlesh reconstructions of extinct hominins are likewise often highly subjective. They may attempt to diminish the intellectual abilities of humans and overstate those of animals. For example, one popular high school textbook caricatures Neanderthals as intellectually primitive even though they exhibited signs of art, language, and culture, and casts Homo erectus as a bungling, stooped form even though its postcranial skeleton is extremely similar to that of modern humans. Conversely, the same textbook portrays an ape-like australopithecine with gleams of human-like intelligence and emotion in its eyes\u2014a tactic common in illustrated books on human origins. University of North Carolina, Charlotte anthropologist Jonathan Marks warns against this when lamenting the \u201cfallacies\u201d of \u201chumanizing apes and ape-ifying humans.\u201d The words of the famed physical anthropologist Earnest A. Hooton from Harvard University still ring true: \u201calleged restorations of ancient types of man have very little, if any, scientific value and are likely only to mislead the public.\u201d
\nGiven these challenges, one might expect caution, humility, and restraint from evolutionary scientists when discussing hypotheses about human origins. And sometimes this is indeed found. But as multiple commentators have recognized, we often find precisely the opposite. Calm and collected scientific objectivity in the field of evolutionary paleoanthropology can be as rare as the fossils themselves. The fragmented nature of the data, combined with the desire of paleoanthropologists to make confident assertions about human evolution, leads to sharp disagreements within the field, as pointed out by Constance Holden in her article in Science titled \u201cThe Politics of Paleoanthropology.\u201d
\nHolden acknowledges that \u201c[t]he primary scientific evidence\u201d relied on by paleoanthropologists \u201cto construct man\u2019s evolutionary history\u201d is \u201ca pitifully small array of bones \u2026 One anthropologist has compared the task to that of reconstructing the plot of War and Peace with 13 randomly selected pages.\u201d According to Holden, it is precisely because researchers must draw their conclusions from this \u201cextremely paltry evidence\u201d that \u201cit is often difficult to separate the personal from the scientific disputes raging in the field.\u201d
\nMake no mistake: The disputes in paleoanthropology are often deeply personal. As Donald Johanson and Blake Edgar admit, ambition and lifelong quests for recognition, funding, and fame, can make it difficult for paleoanthropologists to admit when they are wrong: \u201cThe appearance of discordant evidence is sometimes met with a sturdy reiteration of our original views \u2026 it takes time for us to give up pet theories and assimilate the new information. In the meantime, scientific credibility and funding for more fieldwork hang in the balance.\u201d
\nIndeed, the quest for recognition can inspire outright contempt toward other researchers. After interviewing paleoanthropologists for a documentary in 2002, PBS NOVA producer Mark Davis reported that \u201c[e]ach Neanderthal expert thought the last one I talked to was an idiot, if not an actual Neanderthal.\u201d
\nIt\u2019s no wonder that paleoanthropology is a field rife with dissent and with few universally accepted theories among its practitioners. Even the most established and confidently asserted theories of human origins may be based upon limited and incomplete evidence. In 2001, Nature editor Henry Gee conceded, \u201c[f]ossil evidence of human evolutionary history is fragmentary and open to various interpretations.\u201d<\/p>\n
THE STANDARD STORY OF HUMAN EVOLUTIONARY ORIGINS<\/p>\n
DESPITE THE widespread disagreements and controversies just described, there is a standard story of human origins which is retold in countless textbooks, newsmedia articles, and coffee table books. A representation of the most commonly believed hominin phylogeny is portrayed below in Figure 3-1:<\/p>\n
Figure 3-1: A standard phylogeny of the branch of the hominin tree that includes humans.
\nIllustration: Jonathan Jones.<\/p>\n
Starting with the early hominins at the bottom left, and moving upwards through the australopithecines, and then into members of the genus Homo, this chapter will review the fossil evidence and assess whether it supports this alleged story of human evolution. As we shall see, the evidence\u2014or lack thereof\u2014often gets in the way of the evolutionary story.<\/p>\n
EARLY HOMININ FOSSILS<\/p>\n
ALTHOUGH GIVEN much hype in the media, the earliest hominin fossils are often so fragmentary that they remain the subject of considerable controversy in the scientific community. This section will examine some of the main early hominin fossils and the debates surrounding them.<\/p>\n
Sahelanthropus tchadensis: \u201cToumai Skull\u201d<\/p>\n
Despite the fact that Sahelanthropus tchadensis (also called the \u201cToumai skull\u201d) is known only from one skull and some jaw fragments, it has been called the oldest known hominin that lies directly on the human line.
\nBut not everyone agrees. When the fossil was first reported, Brigitte Senut, a leading researcher at the Natural History Museum in Paris, said \u201cI tend towards thinking this is the skull of a female gorilla.\u201d Writing in Nature with Milford H. Wolpoff, Martin Pickford, and John Hawks, Senut later noted there are \u201cmany \u2026 features that link the specimen with chimpanzees, gorillas or both, to the exclusion of hominids,\u201d and argued \u201cSahelanthropus does not appear to have been an obligate biped.\u201d In their view, \u201cSahelanthropus was an ape.\u201d
\nThis debate has continued, but leading paleoanthropologists have cautioned in the Proceedings of the National Academy of Sciences (USA) that teeth and skull fragments alone are insufficient to properly classify or understand species as a hominin: \u201c[O]ur results show that the type of craniodental characters that have hitherto been used in hominin phylogenetics are probably not reliable for reconstructing the phylogenetic relationships of higher primate species and genera, including those among the hominins.\u201d
\nAt one point during the Texas evolution hearings, Ronald Wetherington testified that \u201cevery fossil we find reinforces the sequence that we had previously supposed to exist rather than suggesting something different.\u201d But this fossil, first reported in 2002, provides a striking counterexample to that assertion. Commenting on the Toumai skull in the journal Nature, Bernard Wood of George Washington University opened by observing, \u201cA single fossil can fundamentally change the way we reconstruct the tree of life.\u201d He went on to state:<\/p>\n
If we accept these as sufficient evidence to classify S. tchadensis as a hominid at the base, or stem, of the modern human clade, then it plays havoc with the tidy model of human origins. Quite simply, a hominid of this age should only just be beginning to show signs of being a hominid. It certainly should not have the face of a hominid less than one-third of its geological age. Also, if it is accepted as a stem hominid, under the tidy model the principle of parsimony dictates that all creatures with more primitive faces (and that is a very long list) would, perforce, have to be excluded from the ancestry of modern humans.<\/p>\n
In other words, if the Toumai skull is accepted as a stem ancestor of humans, then many later supposed human ancestors\u2014including the acclaimed australopithecines\u2014ought not be considered human ancestors. Wood concludes that fossils like Sahelanthropus show \u201ccompelling evidence that our own origins are as complex and as difficult to trace as those of any other group of organisms.\u201d<\/p>\n
Orrorin tugenensis: \u201cOrrorin\u201d<\/p>\n
Orrorin, which means \u201coriginal man\u201d in a local Kenyan language, was a chimpanzee-sized primate which is known only from \u201can assortment of bone fragments,\u201d including pieces of the arm, thigh, and lower jaw, as well as some teeth (Figure 3-2). When initially discovered, the New York Times ran a story titled \u201cFossils May Be Earliest Human Link,\u201d and reported it \u201cmay be the earliest known ancestor of the human family.\u201d Despite the meagerness of the find, enough enthusiasm was stirred that an article in Nature soon after the fossil\u2019s unveiling cautioned that \u201cexcitement needs to be tempered with caution in assessing the claim of a six-million-year-old direct ancestor of modern humans.\u201d<\/p>\n
Figure 3-2: Fragments of Orrorin tugenensis.
\nIllustration: Jonathan Jones.<\/p>\n
Some paleoanthropologists claimed that Orrorin\u2019s femur indicates a bipedal mode of locomotion which was \u201cappropriate for a population standing at the dawn of the human lineage.\u201d But as a later Yale University Press commentary admitted, \u201cAll in all, there is currently precious little evidence bearing on how Orrorin moved.\u201d
\nEvolutionary paleoanthropologists often assume that bipedality is a litmus test for membership along the human line. So if Orrorin did prove to be an upright-walking ape-like creature from six million years ago (mya), would that qualify it as a human ancestor? Not at all. In fact, the fossil record contains bipedal apes which evolutionists recognize were far removed from the human line. In 1999, UC San Diego biologist Christopher Wills observed that \u201c[u]pright posture may not be unique to our own lineage\u201d since \u201c[a]n ape that lived ten million years ago on Sardinia, Oreopithecus bambolii, seems to have acquired similar capabilities, perhaps independently.\u201d A more recent article in ScienceDaily elaborated:<\/p>\n
Oreopithecus bambolii, a fossil ape from Italy shares many similarities with early human ancestors, including features of the skeleton that suggest that it may have been well adapted for walking on two legs. However, the authors observe, enough is known of its anatomy to show that it is a fossil ape that is only distantly related to humans, and that it acquired many \u201chuman-like\u201d features in parallel.<\/p>\n
A 2011 paper in Nature by Bernard Wood and Terry Harrison explains the implications of bipedal apes that had nothing to do with human origins:<\/p>\n
The object lesson that Oreopithecus provides is critical to the debate about interpreting the relationships of the earliest purported hominins. It demonstrates how features considered to be hominin specializations can be shown to have been acquired independently in a non-hominin lineage in association with inferred behaviours that are functionally related to, but not necessarily narrowly restricted to, terrestrial bipedalism.<\/p>\n
Much as the Toumai skull threatened to displace australopithecines from our ancestral line, Pickford and his co-authors argued that if their hypothesis about Orrorin is correct, then australopithecines are again no longer ancestral to humans, but were merely \u201ca side branch of hominid evolution that went extinct.\u201d This hypothesis was not well-received by the paleoanthropological community, because they need the australopithecines to serve as an evolutionary precursor leading to our genus Homo. Another paper in Nature exemplified how dissenting views are treated in paleoanthropology, charging that Pickford\u2019s \u201csimple phylogeny contrasts starkly with mainstream ideas about human evolution, and glosses over many areas of controversy and uncertainty.\u201d
\nWhile Orrorin offers evolutionary paleoanthropologists the tantalizing possibility of a bipedal creature that lived around the time of the supposed split between humans and chimpanzees, simply too little of it is known at present to make confident claims about its locomotion, or its proper place in the supposed evolutionary tree.<\/p>\n
Ardipithecus ramidus: \u201cArdi\u201d<\/p>\n
In 2009, the journal Science announced the publication of long-awaited reports about a 4.4 mya fossil named Ardipithecus ramidus. Expectations were high as its discoverer, UC Berkeley paleoanthropologist Tim White, had previously promised the fossil was a \u201cphenomenal individual\u201d that would be the \u201cRosetta stone for understanding bipedalism.\u201d When the papers were finally released, the science media took it as an opportunity to evangelize the public for Darwin via the fossil they affectionately dubbed \u201cArdi.\u201d<\/p>\n
Figure 3-3: Anterior view of fragmented and reconstructed Ardipithecus ramidus skull.
\nIllustration: Used with permission from American Association for the Advancement of Science, Figure 2(D), Gen Suwa, Berhane Asfaw Reiko T. Kono, Daisuke Kubo4, C. Owen Lovejoy, and Tim D. White, \u201cThe Ardipithecus ramidus Skull and Its Implications for Hominid Origins,\u201d 326 (October 2, 2009): 68e1\u201368e7. Copyright 2009.<\/p>\n
The Discovery Channel ran the headline \u201c \u2018Ardi,\u2019 Oldest Human Ancestor, Unveiled,\u201d and quoted White stating Ardi is \u201cas close as we have ever come to finding the last common ancestor of chimpanzees and humans.\u201d The Associated Press\u2019s headline read \u201cWorld\u2019s oldest human-linked skeleton found,\u201d and stated \u201cthe new find provides evidence that chimps and humans evolved from some long-ago common ancestor.\u201d Science magazine named Ardi the \u201cbreakthough of the year\u201d for 2009, and officially introduced her with an article titled \u201cA New Kind of Ancestor: Ardipithecus Unveiled.\u201d (A reconstruction of Ardi\u2019s skull can be seen in Figure 3-3.)
\nCalling this fossil \u201cnew\u201d may have been a poor word choice on the part of Science, since Ardi was discovered in the early 1990s. Why did it take over 15 years for reports to be published? A 2002 article in Science explains that initially the bones were so \u201csoft,\u201d \u201ccrushed,\u201d \u201csquished,\u201d and \u201cchalky,\u201d that White reported, \u201cwhen I clean an edge it erodes, so I have to mold every one of the broken pieces to reconstruct it.\u201d
\nLater reports similarly acknowledged that \u201csome portions of Ardi\u2019s skeleton were found crushed nearly to smithereens and needed extensive digital reconstruction,\u201d and that its pelvis initially \u201clooked like an Irish stew.\u201d The 2009 report in Science tells a striking story of the fossil\u2019s poor quality: \u201c[T]he team\u2019s excitement was tempered by the skeleton\u2019s terrible condition. The bones literally crumbled when touched. White called it road kill. And parts of the skeleton had been trampled and scattered into more than 100 fragments; the skull was crushed to 4 centimeters in height.\u201d In an article titled \u201cOldest Skeleton of Human Ancestor Found,\u201d the science editor at National Geographic, put it this way: \u201cAfter Ardi died, her remains apparently were trampled down into mud by hippos and other passing herbivores. Millions of years later, erosion brought the badly crushed and distorted bones back to the surface. They were so fragile they would turn to dust at a touch.\u201d
\nClaims about bipedal locomotion in hominids require careful and accurate measurements of the precise shape of various bones. How far should one trust claims about Ardi as a \u201cRosetta stone for understanding bipedalism\u201d when the bones were initially \u201ccrushed to smithereens\u201d and \u201cwould turn to dust at a touch\u201d? Several skeptical paleoanthropologists felt those claims warranted little credence. As Science reported:<\/p>\n
[S]everal researchers aren\u2019t so sure about these inferences. Some are skeptical that the crushed pelvis really shows the anatomical details needed to demonstrate bipedality. The pelvis is \u201csuggestive\u201d of bipedality but not conclusive, says paleoanthropologist Carol Ward of the University of Missouri, Columbia. Also, Ar. ramidus \u201cdoes not appear to have had its knee placed over the ankle, which means that when walking bipedally, it would have had to shift its weight to the side,\u201d she says. Paleoanthropologist William Jungers of Stony Brook University in New York state is also not sure that the skeleton was bipedal. \u201cBelieve me, it\u2019s a unique form of bipedalism,\u201d he says. \u201cThe postcranium alone would not unequivocally signal hominin status, in my opinion.\u201d<\/p>\n
A subsequent paper by primatologist Esteban Sarmiento in Science noted that \u201cAll of the Ar. ramidus bipedal characters cited also serve the mechanical requisites of quadrupedality, and in the case of Ar. ramidus foot-segment proportions, find their closest functional analog to those of gorillas, a terrestrial or semiterrestrial quadruped and not a facultative or habitual biped.\u201d
\nCritics also questioned the claim that Ardi was necessarily ancestral to humans. When Ardi\u2019s reports were first published, Bernard Wood stated, \u201cI think the head is consistent with it being a hominin \u2026 but the rest of the body is much more questionable.\u201d Two years later, Wood co-wrote a paper in Nature elaborating on those criticisms, observing that if \u201cArdipithecus is assumed to be a hominin,\u201d and ancestral to humans, then this implies the fossil had \u201cremarkably high levels of homoplasy among extant great apes.\u201d In other words, Ardi had many ape-like characteristics which, if we set aside the preferences of many evolutionary paleoanthropologists, might imply a much closer relationship to living apes than to humans. According to a ScienceDaily article reporting on Wood\u2019s Nature paper, the claim of Ardi \u201cbeing a human ancestor is by no means the simplest, or most parsimonious explanation.\u201d Stanford University anthropologist Richard Klein put it this way: \u201cI frankly don\u2019t think Ardi was a hominid, or bipedal.\u201d
\nSarmiento observed that Ardi had characters which were different not just from humans, but also from apes. In a Time Magazine interview titled, \u201cArdi: The Human Ancestor Who Wasn\u2019t?,\u201d he elaborated:<\/p>\n
\u201c[Tim White] showed no evidence that Ardi is on the human lineage,\u201d Sarmiento says. \u201cThose characters that he posited as relating exclusively to humans also exist in apes and ape fossils that we consider not to be in the human lineage.\u201d
\nThe biggest mistake White made, according to the paper, was to use outdated characters and concepts to classify Ardi and to fail to identify anatomical clues that would rule her out as a human ancestor. As an example, Sarmiento says that on the base of Ardi\u2019s skull, the inside of the jaw joint surface is open as it is in orangutans and gibbons, and not fused to the rest of the skull as it is in humans and African apes\u2014suggesting that Ardi diverged before this character developed in the common ancestor of humans and apes.<\/p>\n
Whatever Ardi may have been, everyone agrees that this fossil was initially badly crushed and needed extensive reconstruction. Its discoverers adamantly maintain the specimen was a bipedal human ancestor, or something very close to it. No doubt this debate will continue, but are we obligated to take for granted the bold talking points promoted by Ardi\u2019s discoverers in the media? Sarmiento doesn\u2019t think so. According to Time Magazine, he \u201cregards the hype around Ardi to have been overblown.\u201d<\/p>\n
LATER HOMININS: THE AUSTRALOPITHECINES<\/p>\n
IN APRIL 2006, National Geographic ran a story titled \u201cFossil Find Is Missing Link in Human Evolution, Scientists Say,\u201d which reported the discovery of what the Associated Press called \u201cthe most complete chain of human evolution so far.\u201d The fossils, belonging to the species Australopithecus anamensis were said to link Ardipithecus to its supposed australopithecine descendants.
\nWhat exactly was found? According to the technical paper reporting the find, the bold claims were based upon a few fragmented canine teeth which were said to be \u201cintermediate\u201d in size and shape. The technical description used in the paper was intermediate \u201cmasticatory robusticity.\u201d If a couple of four million-year-old teeth of \u201cintermediate\u201d size and shape make \u201cthe most complete chain of human evolution so far,\u201d then the evidence for human evolution must be indeed quite modest.
\nBesides learning to distrust media hype, there is another important lesson to be gained from this episode. Accompanying the praise of this \u201cmissing link\u201d were what might be called retroactive confessions of ignorance. In this common phenomenon, evolutionists acknowledge a severe gap in their evolutionary claims only after they think they have found evidence to plug that gap. Thus, the technical paper that reported these teeth admitted that, \u201cUntil recently, the origins of Australopithecus were obscured by a sparse fossil record,\u201d further stating: \u201cThe origin of Australopithecus, the genus widely interpreted as ancestral to Homo, is a central problem in human evolutionary studies. Australopithecus species differ markedly from extant African apes and candidate ancestral hominids such as Ardipithecus, Orrorin and Sahelanthropus.\u201d Following these comments, an article on MSNBC.com acknowledged that \u201cUntil now, what scientists had were snapshots of human evolution scattered around the world.\u201d
\nEvolutionists who make retroactive confessions of ignorance risk the danger that the evidence which supposedly filled the gap may turn out to not be so compelling after all. This seems to be the case here, where a couple teeth of intermediate \u201cmasticatory robusticity\u201d were apparently all that stood between an unsolved \u201ccentral problem in human evolutionary studies,\u201d and \u201cthe most complete chain of human evolution so far.\u201d
\nMoreover, we\u2019re left with the uncontested admission that the australopithecines \u201cdiffer markedly\u201d from their supposed ancestors\u2014Ardipithecus, Orrorin, or Sahelanthropus. Given the fragmentary and enigmatic nature of those earlier species, a more objective analysis might suspect that this period of supposed early hominin evolution remains what Tim White once called it: \u201ca black hole in the fossil record.\u201d<\/p>\n
Australopithecines Are Like Apes<\/p>\n
While Sahelanthropus, Orrorin, and Ardipithecus are controversial due to the fragmented nature of their remains, there are sufficient known specimens of the australopithecines to gain a better understanding of their morphology. Nonetheless, controversy remains over whether the australopithecines were upright-walking ancestors of the genus Homo.
\nAustralopithecus, which literally means \u201csouthern ape,\u201d is a group of extinct hominins that lived in Africa from a little over 4 mya until about 1 mya. \u201cSplitters\u201d (those paleoanthropologists who tend to see many different species in the fossil record) and \u201clumpers\u201d (those who see fewer) have created a variety of taxonomic schemes for the australopithecines. However, the four most commonly accepted species are afarensis, africanus, robustus, and boisei. Robustus and boisei are larger boned and more \u201crobust\u201d than the others and are sometimes classified under the genus Paranthropus. According to conventional evolutionary thinking, they represent a later-living offshoot that went extinct without leaving any living descendants today. The smaller \u201cgracile\u201d forms, africanus and afarensis (the species which includes the famous fossil \u201cLucy\u201d), lived earlier, and are classified within the genus Australopithecus. These two latter species are commonly said to be directly ancestral to humans.
\nBy far, the most well-known australopithecine fossil is Lucy because she is one of the most complete fossils among known pre-Homo hominins. She is commonly claimed to have been a bipedal ape-like creature which serves as an ideal precursor to the human species.
\nIn 2009, Lucy\u2019s skeleton came to the Pacific Science Center in my hometown of Seattle. Upon entering the room containing the thick glass case holding her bones, I was immediately struck by the incompleteness of her skeleton. Only 40% was found, and a significant percentage is mere rib fragments. (See Figure 3-4.) Very little useful material from Lucy\u2019s skull was recovered, and yet she is one of the most significant specimens ever found.<\/p>\n
Figure 3-4: The skeletal remains of \u201cLucy.\u201d
\nIllustration: Redrawn by Jonathan Jones based on Wikimedia Commons image of Lucy skeleton licensed under Creative Commons Attribution\u2014Share Alike 3.0 Unported license.<\/p>\n
There are some reasons for skepticism over whether \u201cLucy\u201d represents a single individual, or even a single species. In a video playing at the exhibit, Lucy\u2019s discoverer Donald Johanson admitted that when he found the fossil, the bones were scattered across a hillside, where he \u201clooked up the slope and there were other bones sticking out.\u201d Johanson\u2019s written account explains further how the bones were not found together: \u201c[S]ince the fossil wasn\u2019t found in situ, it could have come from anywhere above. There\u2019s no matrix on any of the bones we\u2019ve found either. All you can do is make probability statements.\u201d
\nThis was therefore not a case where the bones were found connected forming a contiguous skeleton, but rather they were scattered across a hillside. Ann Gibbons notes that Johanson\u2019s \u201centire team fanned out over the gully to collect Lucy\u2019s bones.\u201d At one point, Johanson explains that if there had been only one more rainstorm, Lucy\u2019s bones might have been washed away, never to be seen again. This does not inspire confidence in the integrity of the skeleton: If the next rainstorm could have washed Lucy away completely, what might have happened during prior storms to mix her up with who-knows-what? Could \u201cLucy\u201d represent bones from multiple individuals or even multiple species?
\nThe classical rejoinder notes that none of Lucy\u2019s bones appear duplicated, implying they come from a single individual. This is certainly possible, but given the fragmented and the incomplete and scattered nature of the skeleton, the rebuttal argument is far from conclusive. In particular, it\u2019s difficult to say with high confidence that key portions of the skeleton\u2014such as the half-pelvis and half-femur\u2014are from the same individual. The pelvis and femur are, after all, her most studied bones, and are said to indicate she walked upright. As the Pacific Science Center exhibit boldly stated, \u201cLucy\u2019s species walked bipedally, in much the same way as we do,\u201d at one point claiming her skeleton \u201capproximate[s] a chimpanzee-like head perched atop a human-like body.\u201d
\nLucy did have a small, chimp-like head in both size and shape\u2014as University of Witwatersrand paleoanthropologist Lee Berger observes, \u201cLucy\u2019s face would have been prognathic, jutting out almost to the same degree as a modern chimpanzee.\u201d But many have disagreed with claims that she looked like an ape-human hybrid. Bernard Wood refutes this misapprehension: \u201cAustralopithecines are often wrongly thought to have had a mosaic of modern human and modern ape features, or, worse, are regarded as a group of \u2018failed\u2019 humans. Australopithecines were neither of these.\u201d
\nMoreover, many have challenged the claim that Lucy walked like we do, or was even significantly bipedal. Mark Collard and Leslie Aiello observe in Nature that much of the rest of her body was \u201cquite ape-like,\u201d especially with respect to the \u201crelatively long and curved fingers, relatively long arms, and funnel-shaped chest.\u201d Their article also reports \u201cgood evidence\u201d from Lucy\u2019s hand-bones that her species \u201c \u2018knuckle-walked\u2019, as chimps and gorillas do today.\u201d
\nNeedless to say, paleoanthropologists who wish Lucy to be a bipedal precursor to our genus Homo disfavor the \u201cknuckle-walking\u201d interpretation. Collard and Aiello fall into this category, calling this evidence \u201ccounterintuitive,\u201d and suggesting that \u201cthe locomotor repertoire of A. afarensis included forms of bipedalism, climbing and knuckle-walking.\u201d This proposal is tenuous, however, since these forms of locomotion tend to be mutually exclusive. Nonetheless, they dismiss Lucy\u2019s knuckle-walking specializations as \u201cprimitive retentions\u201d from her ancestors. Science writer Jeremy Cherfas explains why this argument is doubtful:<\/p>\n
Everything about her skeleton, from fingertips to toes, suggests that Lucy and her sisters retain several traits that would be very suitable for climbing in trees. Some of those same treeclimbing adaptations can still be detected, albeit much reduced, in much later hominids such as the 2-million-year old specimens of Homo habilis from the Olduvai gorge. It could be argued that Lucy\u2019s arboreal adaptations are just a hangover from her treedwelling past, but animals do not often retain traits that they do not use, and to find those same features in specimens 2 million years later makes it most unlikely that they are remnants.<\/p>\n
Apparently when the evidence points against Lucy being bipedal, it is simply discarded. But the main motivation for this dismissal is the evolutionary belief that modern humans need fully bipedal ape-like ancestors.
\nOther leading paleoanthropologists also acknowledge that Lucy\u2019s mode of locomotion was significantly different from that of humans. Richard Leakey and Roger Lewin argue that A. afarensis and other australopithecines \u201calmost certainly were not adapted to a striding gait and running, as humans are.\u201d Their quotation of anthropologist Peter Schmid\u2019s surprise at the non-human qualities of Lucy\u2019s skeleton is striking:
\n\u201cWe were sent a cast of the Lucy skeleton, and I was asked to assemble it for display,\u201d remembers Peter Schmid, a paleontologist at the Anthropological Institute in Zurich \u2026 \u201cWhen I started to put [Lucy\u2019s] skeleton together, I expected it to look human,\u201d Schmid continues. \u201cEveryone had talked about Lucy as being very modern, very human, so I was surprised by what I saw\u201d \u2026 \u201cWhat you see in Australopithecus is not what you\u2019d want in an efficient bipedal running animal,\u201d says Peter. \u201cThe shoulders were high, and, combined with the funnel-shaped chest, would have made arm swinging very improbable in the human sense. It wouldn\u2019t have been able to lift its thorax for the kind of deep breathing that we do when we run. The abdomen was potbellied, and there was no waist, so that would have restricted the flexibility that\u2019s essential to human running.\u201d<\/p>\n
Figure 3-5: A comparison of Australopithecus (right) to early Homo (left). Black bones indicate those which have been discovered.
\nIllustration: From Figure 1, John Hawks et. al., \u201cPopulation Bottlenecks and Pleistocene Human Evolution,\u201d Molecular Biology and Evolution, copyright 2000, 17 (1): 2\u201322, by permission of the Society for Molecular Biology and Evolution.<\/p>\n
Other studies confirm australopithecine differences with humans, and similarities with apes. Their inner ear canals\u2014responsible for balance and related to locomotion\u2014are different from those of Homo but similar to those of great apes. Their ape-like developmental patterns and ape-like ability for prehensile grasping by their toes led one reviewer in Nature to say that whether australopithecines \u201cwere phylogenetically hominines or not, it seems to me that ecologically they may still be considered as apes.\u201d In 1975 C. E. Oxnard published a paper in Nature using multivariable statistical analysis to compare key australopithecine skeletal characteristics to living hominids. He found that australopithecines have \u201ca mosaic of features unique to themselves and features bearing some resemblances to those of the orangutan\u201d and concluded: \u201cIf these estimates are true, then the possibility that any of the australopithecines is a direct part of human ancestry recedes.\u201d Even the teeth of Lucy\u2019s species have been found to conflict with the hypothesis she was a human ancestor. A 2007 paper in Proceedings of the National Academy of Sciences (USA) reported \u201c[g]orilla-like anatomy on Australopithecus afarensis mandibles,\u201d which was \u201cunexpected,\u201d and \u201ccast[s] doubt on the role of Au. afarensis as a modern human ancestor.\u201d
\nAs for Lucy\u2019s pelvis, many have claimed it supports a bipedal form of locomotion, but Johanson and his team reported it was \u201cbadly crushed\u201d with \u201cdistortion\u201d and \u201ccracking\u201d when first discovered. These problems led one commentator to propose in the Journal of Human Evolution that the reason Lucy\u2019s pelvis is \u201cso different from other australopithecines and so close to the human condition\u201d was \u201cerror in the reconstruction \u2026 creating a very \u2018human-like\u2019 sacral plane.\u201d Another paper in the same journal concluded that the lack of clear fossil data about Lucy prevents paleoanthropologists from making firm conclusions about her mode of locomotion: \u201cPrevailing views of Lucy\u2019s posture are almost impossible to reconcile \u2026 To resolve such differences, more anatomical (fossil) evidence is needed. The available data at present are open to widely different interpretations.\u201d
\nPaleoanthropologist Leslie Aiello, who served as head of the anthropology department at University College London, states that when it comes to locomotion, \u201c[a]ustralopithecines are like apes, and the Homo group are like humans. Something major occurred when Homo evolved, and it wasn\u2019t just in the brain.\u201d
\nThe \u201csomething major\u201d that occurred was the abrupt appearance of the human body plan\u2014without direct evolutionary precursors in the fossil record.<\/p>\n
A BIG BANG THEORY OF HOMO<\/p>\n
IF HUMAN beings evolved from ape-like creatures, what were the transitional species between the ape-like hominins just discussed and the truly human-like members of the Homo genus found in the fossil record?
\nThere aren\u2019t any good candidates.
\nMany paleoanthropologists have cited Homo habilis, dated at about 1.9 mya, as a transitional species between the australopithecines and our genus Homo. But there are many questions about what exactly habiline specimens were. In the words of Ian Tattersall, an anthropologist at the American Museum of Natural History, the species is \u201ca wastebasket taxon, little more than a convenient recipient for a motley assortment of hominin fossils.\u201d As recent as 2009, Tattersall reaffirmed this view, writing with Jeffrey Schwartz that habilis represents \u201ca rather heterogeneous assemblage, and it is probable that more than one hominid species is represented.\u201d
\nPenn State University paleoanthropologist Alan Walker explains the severity of disagreements over this species: \u201c[T]his is not a matter of some fragmentary fossils that are difficult to agree on. Whole crania are placed by different people in different species or even genera.\u201d One reason for the disagreements is that the quality of the fossils is often poor. As Walker puts it, \u201c[d]espite the number of words published on this species \u2026 there is not as much bony evidence as we would like.\u201d
\nIgnoring these difficulties and assuming that H. habilis existed as the species many claim it was, there is a chronological consideration which precludes it from being ancestral to Homo. Habiline remains do not predate the earliest fossil evidence of true members of Homo, which appear about 2 mya. As a consequence, H. habilis could not have been a precursor to our genus.
\nMorphological analyses further confirm that habilis makes an unlikely candidate as an \u201cintermediate\u201d or \u201clink\u201d between Australopithecus and Homo. An authoritative review paper titled \u201cThe Human Genus,\u201d published in Science in 1999 by leading paleoanthropologists Bernard Wood and Mark Collard found that habilis is different from Homo in terms of body size, body shape, mode of locomotion, jaws and teeth, developmental patterns, and brain size, and should be reclassified within Australopithecus. A 2011 article in Science similarly noted that habilis \u201cmatured and moved less like a human and more like an australopithecine,\u201d had a dietary range \u201cmore like Lucy\u2019s than that of H. erectus.\u201d Like the australopithecines, many features of habilis indicate they were more similar to modern apes than humans. According to Wood, habilines \u201cgrew their teeth rapidly, like an African ape, in contrast to the slow dental development of modern humans.\u201d
\nAn analysis in Nature of the ear canals of habilis similarly found that its skull is most similar to baboons and suggested the fossil \u201crelied less on bipedal behaviour than the australopithecines.\u201d The article concluded that \u201c[p]hylogenetically, the unique labyrinth of [the habilis skull] represents an unlikely intermediate between the morphologies seen in the australopithecines and H. erectus.\u201d Additionally, a study by Sigrid Hartwig-Scherer and Robert D. Martin in the Journal of Human Evolution found that the skeleton of habilis was more similar to living apes than were other australopithecines like Lucy. They concluded: \u201cIt is difficult to accept an evolutionary sequence in which Homo habilis, with less human-like locomotor adaptations, is intermediate between Australopithecus afaren[s]is \u2026 and fully bipedal Homo erectus.\u201d Elsewhere, Hartwig-Scherer explained \u201cexpectations concerning postcranial similarities between Homo habilis and later member of the genus Homo could not be corroborated.\u201d
\nTo the contrary, she explains, habilis \u201cdisplays much stronger similarities to African ape limb proportions,\u201d than even Lucy. She called these results \u201cunexpected in view of previous accounts of Homo habilis as a link between australopithecines and humans.\u201d
\nWithout habilis as an intermediate, it is difficult to find fossil hominins to serve as direct transitional forms between the australopithecines and Homo. Rather, the fossil record shows dramatic and abrupt changes which correspond to the appearance of Homo.
\nA 1998 article in Science noted that at about 2 mya, \u201ccranial capacity in Homo began a dramatic trajectory\u201d that resulted in an \u201capproximate doubling in brain size.\u201d Wood and Collard\u2019s review in Science the following year found that only one single trait of one individual hominin fossil species qualified as \u201cintermediate\u201d between Australopithecus and Homo: the brain size of Homo erectus. However, even this one intermediate trait does not necessarily offer any evidence that Homo evolved from less intelligent hominids. As they explain: \u201cRelative brain size does not group the fossil hominins in the same way as the other variables. This pattern suggests that the link between relative brain size and adaptive zone is a complex one.\u201d
\nLikewise, others have shown that intelligence is determined largely by internal brain organization, and is far more complex than the sole variable of brain size. As one paper in the International Journal of Primatology writes, \u201cbrain size may be secondary to the selective advantages of allometric reorganization within the brain.\u201d Thus, finding a few skulls of intermediate size does little to bolster the case that humans evolved from more primitive ancestors. (See Figure 3-6 below.)
\nSimilar to brain size, a study of the pelvic bones of australopithecines and Homo proposed \u201ca period of very rapid evolution corresponding to the emergence of the genus Homo.\u201d In fact, a paper in the Journal of Molecular Biology and Evolution found that Homo and Australopithecus differ significantly in brain size, dental function, increased cranial buttressing, expanded body height, visual, and respiratory changes and stated: \u201cWe, like many others, interpret the anatomical evidence to show that early H. sapiens was significantly and dramatically different from \u2026 australopithecines in virtually every element of its skeleton and every remnant of its behavior.\u201d<\/p>\n
Figure 3-6: Got a big head? Don\u2019t get a big head. Brain size is not always a good indicator of intelligence or evolutionary relationships. Case in point: Neanderthals had a larger average skull size than modern humans. Moreover, skull size can vary greatly within an individual species. (See Figure 3-8.) Given the range of modern human genetic variation, a progression of relatively small to very large skulls could be created by using the bones of living humans alone. This could give the misimpression of some evolutionary lineage when in fact it is merely the intepretation of data by preconceived notions of what happened. The lesson is this: don\u2019t be too impressed when textbooks, news stories, or TV documentaries display skulls lined up from small sizes to larger ones.
\nIllustration: Jonathan Jones<\/p>\n
Noting these many changes, the study called the origin of humans, \u201ca real acceleration of evolutionary change from the more slowly changing pace of australopithecine evolution\u201d and stated that such a transformation would have included radical changes: \u201cThe anatomy of the earliest H. sapiens sample indicates significant modifications of the ancestral genome and is not simply an extension of evolutionary trends in an earlier australopithecine lineage throughout the Pliocene. In fact, its combination of features never appears earlier.\u201d
\nThese rapid, unique, and genetically significant changes are termed \u201ca genetic revolution\u201d where \u201cno australopithecine species is obviously transitional.\u201d For those not constrained by an evolutionary paradigm, what is also not obvious is that this transition took place at all. The lack of fossil evidence for this hypothesized transition is confirmed by Harvard paleoanthropologists Daniel E. Lieberman, David R. Pilbeam, and Richard W. Wrangham, who provide a stark analysis of the lack of evidence for a transition from Australopithecus to Homo:<\/p>\n
Of the various transitions that occurred during human evolution, the transition from Australopithecus to Homo was undoubtedly one of the most critical in its magnitude and consequences. As with many key evolutionary events, there is both good and bad news. First, the bad news is that many details of this transition are obscure because of the paucity of the fossil and archaeological records.<\/p>\n
As for the \u201cgood news,\u201d they still admit: \u201c[A]lthough we lack many details about exactly how, when, and where the transition occurred from Australopithecus to Homo, we have sufficient data from before and after the transition to make some inferences about the overall nature of key changes that did occur.\u201d
\nIn other words, the fossil record provides ape-like australopithecines, and human-like Homo, but not fossils documenting a transition between them.
\nIn the absence of fossil evidence, evolutionary claims about the transition to Homo are said to be mere \u201cinferences\u201d made by studying the non-transitional fossils we do have, and then assuming that a transition must have occurred somehow, sometime, and someplace.
\nAgain, this does not make for a compelling evolutionary account of human origins. Ian Tattersall also acknowledges the lack of evidence for a transition to humans:<\/p>\n
Our biological history has been one of sporadic events rather than gradual accretions. Over the past five million years, new hominid species have regularly emerged, competed, coexisted, colonized new environments and succeeded\u2014or failed. We have only the dimmest of perceptions of how this dramatic history of innovation and interaction unfolded \u2026<\/p>\n
Likewise, evolutionary biologist Ernst Mayr recognized our abrupt appearance when he wrote in 2004:<\/p>\n
The earliest fossils of Homo, Homo rudolfensis and Homo erectus, are separated from Australopithecus by a large, unbridged gap. How can we explain this seeming saltation? Not having any fossils that can serve as missing links, we have to fall back on the time-honored method of historical science, the construction of a historical narrative.<\/p>\n
As another commentator proposed, the evidence implies a \u201cbig bang theory\u201d of the appearance of our genus Homo.<\/p>\n
Figure 3-7: A comparison of skulls from Homo erectus (A), Homo neanderthalensis (B), and Homo sapiens (C).
\nIllustration: Adapted from Wikimedia Commons work in the public domain.<\/p>\n
ALL IN THE FAMILY<\/p>\n
IN CONTRAST to the australopithecines, the major members of Homo\u2014such as erectus and the Neanderthals (Homo neanderthalensis)\u2014are very similar to modern humans. (See comparison of skulls in Figure 3-7.) They\u2019re so similar to us that some paleoanthropologists have classified erectus and neanderthalensis as members of our own species, Homo sapiens.
\nHomo erectus appears in the fossil record a little over 2 mya. The name Homo erectus means \u201cupright man,\u201d and unsurprisingly, below the neck they were extremely similar to us. Indeed, in contrast to the australopithecines and habilines, Homo erectus is the \u201cearliest species to demonstrate the modern human semicircular canal morphology,\u201d previously noted as a feature indicative of the mode of locomotion. Another study found that total energy expenditure (TEE), a complex character related to body size, diet quality, and food-gathering activity, \u201cincreased substantially in Homo erectus relative to the earlier australopithecines,\u201d beginning to approach the very high TEE value of modern humans. As one paper in a 2007 Oxford University press volume notes, \u201cdespite having smaller teeth and jaws, H. erectus was a much bigger animal than the australopithecines, being humanlike in its stature, body mass, and body proportions.\u201d While the average brain-size of Homo erectus is less than modern humans, erectus cranial capacities are well within the range of normal human variation (Figure 3-8).<\/p>\n
Figure 3-8. Cranial Capacities of Extant and Extinct Hominids
\nTAXON
\nCRANIAL CAPACITIES
\nTAXON RESEMBLES
\nGorilla (Gorilla gorilla)
\n340\u2013752 cc
\nModern Apes
\nChimpanzee (Pan troglodytes)
\n275\u2013500 cc
\nAustralopithecus
\n370\u2013515 cc (Avg. 457 cc)
\nHomo habilis
\nAvg. 552 cc
\nHomo erectus
\n850\u20131250 cc (Avg. 1016 cc)
\nModern Humans
\nNeanderthals
\n1100\u20131700 cc (Avg. 1450 cc)
\nHomo sapiens
\n800\u20132200 cc (Avg. 1345 cc)<\/p>\n
Donald Johanson suggests that were erectus alive today, it could mate successfully with modern humans to produce fertile offspring. In other words, were it not for our separation by time, we might be considered biologically as interbreeding members of the same species.
\nThough Neanderthals have been stereotyped as bungling, primitive precursors to modern humans, in reality, they were so similar to us that if a Neanderthal walked past you on the street, you probably wouldn\u2019t notice many differences. Wood and Collard make this same point in drier, more technical language: \u201cThe numerous associated skeletons of H. neanderthalensis indicate that their body shape was within the range of variation seen in modern humans.\u201d
\nWashington University paleoanthropologist Erik Trinkaus likewise argues: \u201cThey may have had heavier brows or broader noses or stockier builds, but behaviorally, socially and reproductively they were all just people.\u201d In a 2007 Washington Post interview, Trinkaus dispelled the myth that Neanderthals were intellectually inferior:<\/p>\n
Although Neanderthals live in the public imagination as hulking and slow-witted \u201cAlley Oops,\u201d Trinkaus and others say there is no reason to believe they were any less intelligent than the newly arrived \u2018modern humans.\u2019 Neanderthals were stockier and had larger brows, sharper teeth and more jutting jaws, but their brain capacity appears to have been no different than that of the newcomers.<\/p>\n
But it isn\u2019t just the \u201cpublic imagination\u201d which has wrongly cast Neanderthals as unintelligent brutes. A 2003 article in Smithsonian magazine traces these myths back to prior European anthropologists, who, inspired by Darwin, wrongly promoted the \u201csubhuman\u201d view:<\/p>\n
\u201cIn the minds of the European anthropologists who first studied them, Neanderthals were the embodiment of primitive humans, subhumans if you will,\u201d says Fred H. Smith, a physical anthropologist at Loyola University in Chicago who has been studying Neanderthal DNA. \u201cThey were believed to be scavengers who made primitive tools and were incapable of language or symbolic thought.\u201d Now, he says, researchers believe that Neanderthals \u201cwere highly intelligent, able to adapt to a wide variety of ecological zones, and capable of developing highly functional tools to help them do so. They were quite accomplished.\u201d<\/p>\n
University of Bordeaux archaeologist Francesco d\u2019Errico affirms these comments, stating, \u201cNeanderthals were using technology as advanced as that of contemporary anatomically modern humans and were using symbolism in much the same way.\u201d
\nHard evidence backs up these claims. Anthropologist Stephen Molnar explains that \u201cthe estimated mean size of [Neanderthal] cranial capacity (1,450 cc) is actually higher than the mean for modern humans (1,345 cc).\u201d One paper in Nature suggested, \u201cthe morphological basis for human speech capability appears to have been fully developed\u201d in Neanderthals. Indeed, Neanderthal remains have with been found associated with signs of culture including art, burial of their dead, and technology including the usage of complex tools. At least one artifact shows Neanderthals made musical instruments like the flute. While this example might be dated and uncertain, there is even a report in Nature from 1908 which claims to have discovered a Neanderthal type skeleton wearing chain mail armor. Whether that report is right or wrong, it is clear Neanderthals were not intellectually dissimilar from their \u201chuman\u201d contemporaries. As experimental archaeologist Metin Eren said, when it came to making tools, \u201cin many ways, Neanderthals were just as smart or just as good as us.\u201d Likewise, Trinkaus says that when comparing ancient Europeans and Neanderthals: \u201cBoth groups would seem to us dirty and smelly but, cleaned up, we would understand both to be human. There\u2019s good reason to think that they did as well.\u201d
\nOne of these good reasons is the presence of \u201cmorphological mosaics\u2014skeletons showing a mix of modern human and Neanderthal traits which indicate \u201cthat Neandertals and modern humans are members of the same species who interbred freely.\u201d In 2010, Nature reported the finding of Neanderthal DNA markers in living humans: \u201cA genetic analysis of nearly 2,000 people from around the world indicates that such extinct species interbred with the ancestors of modern humans twice, leaving their genes within the DNA of people today.\u201d In the words of Jeffrey Long, a genetic anthropologist at the University of New Mexico, \u201cNeanderthals didn\u2019t completely disappear\u201d because \u201c[t]here is a little bit of Neanderthal leftover in almost all humans.\u201d Unsurprisingly, these observations have led to proposals that Neanderthals were a sub-race of our own species.
\nWe saw earlier that Leslie Aiello said \u201cAustralopithecines are like apes, and the Homo group are like humans.\u201d This is consistent with what we see in the major members of Homo like H. erectus and Neanderthals. According to Siegrid Hartwig-Scherer, the differences between these humanlike members of the genus Homo can be explained as microevolutionary effects of \u201csize variation, climatic stress, genetic drift and differential expression of [common] genes.\u201d These small differences do not supply evidence of the evolution of humans from earlier ape-like creatures.<\/p>\n
CONCLUSION<\/p>\n
WHILE VIRTUALLY the entire hominin fossil record is marked by incomplete and fragmented fossils, about 3\u20134 mya we see ape-like australopithecines appearing suddenly. When the genus Homo appears around 2 mya, it also does so in an abrupt fashion, without clear evidence of a transition from previous ape-like hominins. Subsequent members of the genus Homo appear very similar to modern humans, and their differences amount to small-scale microevolutionary changes.
\nAt the beginning of this chapter I quoted SMU anthropologist Ronald Wetherington telling the Texas State Board of Education that the fossil record shows an unbroken sequence documenting our gradual Darwinian evolution from ape-like species. Were we to revise Wetherington\u2019s testimony in light of the actual evidence discussed in the technical literature, we might say that the hominin fossil record is anything but unbroken. There are many gaps and virtually no plausible transitional fossils that are generally accepted, even by evolutionists, to be direct human ancestors.
\nThus, public claims of evolutionists to the contrary, the appearance of humans in the fossil record appears to have been anything but a gradual Darwinian evolutionary process. The Darwinian belief that humans evolved from apelike species requires inferences that go beyond the evidence and is not supported by the fossil record.<\/p>\n
4<\/p>\n
FRANCIS COLLINS, JUNK DNA, AND CHROMOSOMAL FUSION<\/p>\n
Casey Luskin<\/p>\n
Leading proponents of \u201ctheistic evolution\u201d like Francis Collins offer two primary genetic arguments for human\/ape common ancestry: \u201cjunk\u201d DNA and chromosomal fusion. The argument from junk DNA fails because most non-coding DNA has important cellular functions and is not \u201cjunk.\u201d The argument from chromosomal fusion fails because at most it indicates that humans experienced a fusion event, but says nothing about whether our lineage leads back to a common ancestor with apes.<\/p>\n
IN HIS BEST-SELLING BOOK THE LANGUAGE OF GOD (2006), GENETICIST Francis Collins claims that human DNA provides \u201cpowerful support for Darwin\u2019s theory of evolution, that is descent from a common ancestor with natural selection operating on randomly occurring variations.\u201d More specifically, he argues that our DNA demonstrates that humans and apes share a common ancestor.
\nFormerly the head of the Human Genome Project, Collins is well-known as an evangelical Christian who embraces both Darwinian evolution and embryonic stem cell research. With the help of a $2 million grant from the John Templeton Foundation in 2008, Collins co-founded the BioLogos Foundation with the purpose of persuading Christian leaders and laypeople to accept biological evolution. Collins had to step down from the group after being appointed director of the National Institutes of Health by President Barack Obama, but his emphatic defense of ape\/human common ancestry still has wide influence in the faith community.
\nCollins offers two main DNA-based arguments for his claim that humans share a common ancestor with apes and other animals. First, non-coding DNA shared by humans and other mammals is supposedly functionless junk, which according to Collins means \u201cthe conclusion of a common ancestor for humans and mice is virtually inescapable.\u201d Second, human chromosome #2 resulted from the fusion of two chromosomes like those found in apes\u2014evidence which Collins claims is \u201cvery difficult to understand \u2026 without postulating a common ancestor\u201d between humans and apes.
\nThese are common evolutionary arguments for ape\/human common ancestry, but as this chapter will show, Collins\u2019s case is based largely on outdated science and questionable assumptions. To be specific:<\/p>\n
\u2022 Numerous studies have found extensive evidence of function for non-coding DNA, showing that it is not genetic \u201cjunk\u201d after all.<\/p>\n
\u2022 Human chromosomal fusion may imply that the human lineage experienced a fusion event, but this tells us nothing about whether our lineage extends back to share a common ancestor with apes. Moreover, the genetic evidence for human chromosomal fusion isn\u2019t nearly as strong as Collins and others make it out to be.<\/p>\n
In sum, the evidence from DNA does not establish Collins\u2019s conclusions about human evolution.<\/p>\n
NON-CODING DNA: NOT REALLY \u201cJUNK\u201d AFTER ALL?<\/p>\n
To HIS credit, Collins avoids the usual simplistic argument that shared functional genetic similarity between two species must demonstrate they shared a common ancestor, acknowledging that functional genetic similarity \u201calone does not, of course, prove a common ancestor\u201d because a designer could have \u201cused successful design principles over and over again.\u201d Instead, Collins offers a different argument. He cites a type of DNA called ancient repetitive elements (AREs) as allegedly non-functional \u201cjunk\u201d DNA, which in his view demonstrates both Darwinian evolution and human\/ape common ancestry.
\nRepetitive elements are common in mammalian genomes. We have them. Apes have them. Mice have them. And we often share them in the same places in our genomes. Collins asserts that AREs are \u201cgenetic flotsam and jetsam\u201d which \u201cpresen[t] an overwhelming challenge to those who hold to the idea that all species were created ex nihilo.\u201d In his view, \u201c[u]nless one is willing to take the position that God has placed these decapitated AREs in these precise positions to confuse and mislead us, the conclusion of a common ancestor for humans and mice is virtually inescapable.\u201d Sounding much like Collins, atheist Darwinist Richard Dawkins likewise writes that \u201ccreationists might spend some earnest time speculating on why the Creator should bother to litter genomes with \u2026 junk tandem repeat DNA.\u201d It\u2019s worth noting that both Collins and Dawkins are making a theological argument (basically, \u201cGod wouldn\u2019t do it that way\u201d) as much as a scientific claim. I will leave the soundness of their theology to others, but their science has been overturned by the evidence.
\nContrary to both Collins and Dawkins, even a cursory review of the scientific literature shows it is wildly inappropriate to simply assume that repetitive DNA\u2014or most others types of non-coding DNA\u2014are useless genetic \u201cjunk.\u201d
\nOpen-minded scientists understood this long before Collins wrote his book. In 2002, biologist Richard Sternberg surveyed the literature and found extensive evidence for functions for AREs. Writing in the Annals of the New York Academy of Sciences, he found that ARE functions include:<\/p>\n
\u2022 Satellite repeats forming higher-order nuclear structures<\/p>\n
\u2022 Satellite repeats forming centromeres<\/p>\n
\u2022 Satellite repeats and other REs involved in chromatin condensation<\/p>\n
\u2022 Telomeric tandem repeats and LINE elements<\/p>\n
\u2022 Subtelomeric nuclear positioning\/chromatin boundary elements<\/p>\n
\u2022 Non-TE interspersed chromatin boundary elements<\/p>\n
\u2022 Short, interspersed nuclear elements or SINEs as nucleation centers for methylation<\/p>\n
\u2022 SINEs as chromatin boundary\/insulator elements SINEs involved in cell proliferation<\/p>\n
\u2022 SINEs involved in cellular stress responses<\/p>\n
\u2022 SINEs involved in translation (may be connected to stress response)<\/p>\n
\u2022 SINEs involved in binding cohesin to chromosomes<\/p>\n
\u2022 LINEs involved in DNA repair<\/p>\n
Sternberg concluded that \u201cthe selfish [junk] DNA narrative and allied frameworks must join the other \u2018icons\u2019 of neo-Darwinian evolutionary theory that, despite their variance with empirical evidence, nevertheless persist in the literature.\u201d
\nOther genetic research has continued to uncover functions for various types of repetitive DNA, including SINE, LINE, and Alu elements. One paper even suggested that repetitive Alu sequences might be involved in \u201cthe development of higher brain function\u201d in humans. Numerous other functions have been discovered for various types of non-coding DNA, including:<\/p>\n
\u2022 Repairing DNA<\/p>\n
\u2022 Assisting in DNA replication<\/p>\n
\u2022 Regulating DNA transcription<\/p>\n
\u2022 Aiding in folding and maintenance of chromosomes<\/p>\n
\u2022 Controlling RNA editing and splicing<\/p>\n
\u2022 Helping to fight disease<\/p>\n
\u2022 Regulating embryological development<\/p>\n
Sternberg, along with University of Chicago geneticist James Shapiro, predicted in 2005 that \u201cone day, we will think of what used to be called \u2018junk DNA\u2019 as a critical component of truly \u2018expert\u2019 cellular control regimes.\u201d
\nThe day foreseen by Sternberg and Shapiro may have come sooner than they expected. In 2007, the Washington Post reported that a huge scientific consortium, the ENCODE project, discovered that \u201cthe vast majority of the 3 billion \u2018letters\u2019 of the human genetic code are busily toiling at an array of previously invisible tasks.\u201d According to an article in Nature reporting on the project:<\/p>\n
Biology\u2019s new glimpse at a universe of non-coding DNA\u2014what used to be called \u2018junk\u2019 DNA\u2014has been fascinating and befuddling. Researchers from an international collaborative project called the Encyclopedia of DNA Elements (ENCODE) showed that in a selected portion of the genome containing just a few per cent of protein-coding sequence, between 74% and 93% of DNA was transcribed into RNA. Much non-coding DNA has a regulatory role; small RNAs of different varieties seem to control gene expression at the level of both DNA and RNA transcripts in ways that are still only beginning to become clear.<\/p>\n
A 2007 paper in Nature Reviews Genetics, titled \u201cGenome-wide transcription and the implications for genomic organization,\u201d explains the extensive, complex, and vital nature of these mysterious functions of non-coding DNA:<\/p>\n
Evidence indicates that most of both strands of the human genome might be transcribed, implying extensive overlap of transcriptional units and regulatory elements. These observations suggest that genomic architecture is not colinear, but is instead interleaved and modular, and that the same genomic sequences are multifunctional: that is, used for multiple independently regulated transcripts and as regulatory regions.<\/p>\n
Likewise, a 2008 paper in Science found that almost all parts of well-studied eukaryotic genomes are transcribed, yielding immense amounts of non-protein-coding strands of RNA which likely have functions:<\/p>\n
The past few years have revealed that the genomes of all studied eukaryotes are almost entirely transcribed, generating an enormous number of non-protein-coding RNAs (ncRNAs). In parallel, it is increasingly evident that many of these RNAs have regulatory functions. Here, we highlight recent advances that illustrate the diversity of ncRNA control of genome dynamics, cell biology, and developmental programming.<\/p>\n
The paper goes on to elaborate specifically that repetitive elements play important roles in this cellular control: \u201cGiven the abundance of transcribed repetitive sequences, this may represent a genome-wide strategy for the control of chromatin domains that may be conserved throughout eukaryotes.\u201d
\nA 2003 article in Science acknowledged that \u201cjunk DNA\u201d labels\u2014similar to those used by Collins\u2014have discouraged scientists from discovering the functions of noncoding repetitive elements:<\/p>\n
Although catchy, the term \u2018junk DNA\u2019 for many years repelled mainstream researchers from studying noncoding DNA. Who, except a small number of genomic clochards, would like to dig through genomic garbage? However, in science as in normal life, there are some clochards who, at the risk of being ridiculed, explore unpopular territories. Because of them, the view of junk DNA, especially repetitive elements, began to change in the early 1990s. Now, more and more biologists regard repetitive elements as a genomic treasure.<\/p>\n
Despite widespread Darwinian assumptions to the contrary, the paper concluded that, \u201crepetitive elements are not useless junk DNA but rather are important, integral components of eukaryotic genomes.\u201d
\nIn addition to repetitive elements, another kind of \u201cjunk\u201d DNA appealed to by Collins to support ape\/human common ancestry is the \u201cpseudogene.\u201d
\nCollins writes in The Language of God that a pseudogene in humans (caspase-12) is functionless and asks, \u201cwhy would God have gone to the trouble of inserting such a nonfunctional gene in this precise location?\u201d He makes this same type of argument in his later book, The Language of Science and Faith (2011), citing a supposedly functionless vitamin C pseudogene in humans: \u201cTo claim that the human genome was created by God independently, rather than having descended from a common ancestor, means God inserted a broken piece of DNA into our genomes. This is not remotely plausible.\u201d Similarly, Brown University biologist Kenneth Miller has cited such pseudogenes as \u201ccase-closed\u201d evidence because \u201ccommon ancestry is the only possible explanation for so many matching errors in the same gene.\u201d
\nBut are pseudogenes really functionless, broken DNA?
\nAs with AREs, multiple functions for pseudogenes have been discovered. In fact, two leading biologists writing in Annual Review of Genetics reported that \u201cpseudogenes that have been suitably investigated often exhibit functional roles.\u201d Likewise, a 2011 paper in the journal RNA titled \u201cPseudogenes: Pseudo-functional or key regulators in health and disease?\u201d argues they should no longer be presumed \u201cjunk\u201d: \u201cPseudogenes have long been labeled as \u2018junk\u2019 DNA, failed copies of genes that arise during the evolution of genomes. However, recent results are challenging this moniker; indeed, some pseudogenes appear to harbor the potential to regulate their protein-coding cousins.\u201d
\nIndeed, one study suggested that even the caspase-12 pseudogene which Collins cites can produce a \u201cCARD-only protein,\u201d a type of functional proteins in humans. The study suggests that human caspase-12 interacts in some biological pathways, and encourages scientists to study the caspase-12 pseudogene to understand its function: \u201cSince human pseudo-caspase-12 is structurally comparable to ICEBERG and COP\/Pseudo-ICE [CARD-only proteins], it would be interesting to study its involvement in similar pathways.\u201d
\nWhile there is much we still don\u2019t know about noncoding DNA, Collins was wrong to simply assume that the vast majority of repetitive DNA is functionless \u201cgenetic flotsam and jetsam\u201d or that pseudogenes are \u201cbroken\u201d DNA. A genomic revolution in the past 5\u201310 years has uncovered numerous functions for non-coding DNA elements. Ironically, Collins himself participated in some of this research as head of the Human Genome Project. Perhaps that is why the year following The Language of God Collins started to pull back on his public promotion of the idea of junk DNA, even telling one reporter that he had \u201cstopped using the term.\u201d
\nDespite Collins\u2019s apparent backtracking, the BioLogos Foundation he co-founded has continued to champion the junk DNA paradigm to members of the faith community as a reason they should embrace biological evolution. In reality, junk DNA is an increasingly outdated way to look at non-coding DNA, and its usefulness in proving common ancestry of humans with apes is highly suspect.<\/p>\n
CHROMOSOMAL FUSION WITHOUT COMMON ANCESTRY<\/p>\n
THE SECOND main argument for human\/ape common ancestry made by Francis Collins is his claim that human chromosome #2 has a structure similar to what one would expect if two chimpanzee chromosomes became fused, end to end. Humans have 23 pairs of chromosomes, but chimps and other great apes have 24. In The Language of God, Collins argues that this chromosomal fusion explains why humans have one less pair of chromosomes than apes, claiming \u201cit is very difficult to understand this observation without postulating a common ancestor.\u201d
\nTo the contrary, it is very easy to understand this evidence without postulating a common ancestor.
\nAssuming that human chromosome 2 is fused as Collins claims it is, human chromosomal fusion merely shows that at some point within our lineage, two chromosomes became fused. Logically speaking, this evidence tells us nothing about whether our human lineage leads back to a common ancestor with apes. Nor does it tell us whether the earliest humans were somehow ape-like.
\nEven if our ancestors did once have 24 pairs of chromosomes, they still could have been essentially just like fully modern humans. As University of North Carolina, Charlotte anthropologist Jonathan Marks observes, \u201cthe fusion isn\u2019t what gives us language, or bipedalism, or a big brain, or art, or sugarless bubble gum. It\u2019s just one of those neutral changes, lacking outward expression and neither good nor bad.\u201d At best, the evidence for human chromosomal fusion implies that one of our ancestors experienced a chromosomal fusion event which then got fixed into the human population; but this evidence tells us nothing about whether we share a common ancestor with apes.
\nThe evidence for human chromosomal fusion does not provide special evidence that humans share a common ancestor with chimps. The evidence is equally compatible with common descent (A) or common design (B) where there is no shared ancestry between the species.
\nIf we step outside of the Darwinian box, the following scenario becomes equally possible with common ancestry:<\/p>\n
1. The human lineage was designed separately from apes.
\n2. A chromosomal fusion event occurred in our lineage.
\n3. The trait spread throughout the human population during a genetic bottleneck (when the human population size suddenly became quite small)<\/p>\n
In such a scenario, the evidence would appear precisely as we find it, without any common ancestry with apes, as explained by the two models described in Figure 4-1 on the next page.
\nIn Model A, humans and chimps share a common ancestor, and the human line experienced a chromosomal fusion event. This is the standard evolutionary model promoted by Francis Collins.
\nHowever, Model B is equally compatible with the observed data. In Model B, humans and apes do not share a common ancestor, and the human line experienced a chromosomal fusion event. This model shows that it is quite easy to explain the chromosomal fusion evidence without postulating a common ancestor without any common ancestry with apes.<\/p>\n
Figure 4-1: Two models for understanding human chromosomal fusion.
\nIllustration: Casey Luskin<\/p>\n
To further illustrate why chromosomal fusion does not demonstrate common ancestry between humans and apes, consider the following hypothetical situation.
\nImagine that in the year 2050, a small, isolated human tribe experiences a second chromosomal fusion event (they remain fertile and otherwise normal). We\u2019ll call them the \u201cDoublefuser\u201d people. In 2100, war, sickness, and famine destroy the rest of humanity. But the Doublefusers survive and repopulate the earth, rediscovering genetics and evolution. Eventually, the Doublefusers develop technology to examine their own chromosomes and their scientists exclaim, \u201cWe Doublefusers have 22 pairs of chromosomes, including two pairs of fused chromosomes. Since apes have 24 pairs of chromosomes, we must be descended from ape-like creatures with 48 chromosomes!\u201d
\nFrom our vantage, we see that the Doublefusers\u2019 second chromosomal fusion event took place recently, far removed from any common ancestor between humans and chimps, and offers little logical reason to infer human-chimp common ancestry. Why should we assume the case must be any different with our one fused chromosome? Yet many Darwinian evolutionists mistakenly view our one pair of fused chromosomes precisely as the Doublefusers view their two pairs of fused chromosomes.
\nThe Darwinian might respond by saying: \u201cThe fusion evidence shows our ancestors once had 48 chromosomes, like chimpanzees and other great apes do today. Moreover, our fused chromosome #2 even contains segments resembling ape chromosomes 2a and 2b. Common ancestry would have predicted all this evidence.\u201d But the Darwinian rejoinder merely restates the fact that humans and apes share a highly similar genetic structure. This high level of human\/chimp functional genetic similarity does not demonstrate common ancestry. In Chapter 1, Ann Gauger has already elaborated why shared human\/chimp functional genetic similarity does not necessarily demonstrate common ancestry: Functional genetic similarities might result from functional requirements and common design rather than inheritance from a common ancestor. Indeed, as we have seen, even Francis Collins admits that functional genetic similarity \u201calone does not, of course, prove a common ancestor\u201d because a designer could have \u201cused successful design principles over and over again.\u201d
\nAt most, the chromosomal fusion evidence strengthens something we already knew\u2014that chimps and humans have high genetic similarity. Such functional similarities may just as easily be the result of functional requirements implemented via common design.
\nThus far we have assumed that there really was a fusion event in human genetic history. But how strong is the actual evidence for this contention?
\nWhen using chromosomal fusion to argue for human\/chimp common ancestry, biologist Kenneth R. Miller claims that \u201c[t]he forensic case of the missing chromosome is settled beyond any doubt.\u201d But in fact, the evidence for chromosomal fusion isn\u2019t nearly as clear-cut as evolutionists like Miller claim.
\nTelomeric DNA at the ends of our chromosomes normally consists of thousands of repeats of the 6-base-pair sequence TTAGGG. But the alleged fusion point in human chromosome 2 contains far less telomeric DNA than it should if two chromosomes were fused end-to-end: As evolutionary biologist Daniel Fairbanks admits, the location only has 158 repeats, and only \u201c44 are perfect copies\u201d of the sequence.
\nAdditionally, a paper in Genome Research found that the alleged telomeric sequences we do have are \u201cdegenerated significantly\u201d and \u201chighly diverged from the prototypic telomeric repeats.\u201d The paper is surprised at this finding, because the fusion event supposedly happened recently\u2014much too recent for such dramatic divergence of sequence. Thus, the paper asks: \u201cIf the fusion occurred within the telomeric repeat arrays less than ~6 mya [million years ago], why are the arrays at the fusion site so degenerate?\u201d The conclusion is this: If two chromosomes were fused end-to-end in humans, then a huge amount of alleged telomeric DNA is missing or garbled.
\nFinally, the presence of telomeric DNA within a mammalian chromosome isn\u2019t highly unusual, and does not necessarily indicate some ancient point of fusion of two chromosomes. Evolutionary biologist Richard Sternberg points out that interstitial telomeric sequences (ITSs) are commonly found throughout mammalian genomes, but the telomeric sequences within human chromosome 2 are cherry-picked by evolutionists and cited as evidence for a fusion event:<\/p>\n
[O]f all the known ITSs, and there are many in the genomes of chimps and humans, as well as mice and rats and cows \u2026 the 2q13 ITS is the only one that can be associated with an evolutionary breakpoint or fusion. The other ITSs, I hasten to add, do not square up with chromosomal breakpoints in primates. In brief, to hone in on the 2q13 ITS as being typical of what we see in the human and chimp genomes seems almost like cherry-picking data. Most are not DNA scars in the way they have been portrayed.<\/p>\n
Thus, there are at least three reasons why the evidence isn\u2019t exactly what the fusion story predicts:<\/p>\n
\u2022 The alleged fusion point in chromosome 2 contains much less telomeric DNA than it should<\/p>\n
\u2022 The supposed telomeric sequences we do have are highly \u201cdegenerate\u201d and \u201chighly diverged\u201d from what we would expect if there were a relatively recent fusion event<\/p>\n
\u2022 Finding interstitial telomeric DNA in mammals isn\u2019t all that remarkable, and doesn\u2019t necessarily indicate a fusion event<\/p>\n
But\u2014and this is the key point\u2014even if human chromosome #2 is the result of two other chromosomes which became fused, this is not evidence for human\/ape common ancestry. At most, it shows our human lineage experienced a chromosomal fusion event, but it does not tell us whether our lineage leads back to a common ancestor with apes.<\/p>\n
CONCLUSION<\/p>\n
IN RECENT years, genetic arguments have been offered to the public as definitive new proof that human beings share a common ancestor with apes and other animals. Francis Collins has been at the forefront of popularizing such arguments, especially in the faith community. According to Collins, there is no longer any room for disagreement: \u201cThe study of genomes leads inexorably to the conclusion that we humans share a common ancestor with other living things.\u201d Indeed, not only is the idea of human\/ape common ancestry beyond dispute, but \u201cthe conclusion of a common ancestor for humans and mice is virtually inescapable.\u201d
\nYet for all of Collins\u2019s use of terms like \u201cinexorably\u201d and \u201cinescapable,\u201d the fact remains that the evidence he presents based on genetics simply does not show what he claims.
\nAt best, the evidence discussed in this chapter reaffirms something we already knew: that humans and chimps share similar functional genetic sequences. But this can be explained by common design just as well as by common descent. What else is left? Not much.
\nAs we have seen, Collins\u2019s arguments from junk DNA are being eroded with each passing month by new studies uncovering a myriad of functions for non-coding DNA. In particular, biologists are finding extensive evidence of function for noncoding elements like ancient repetitive DNA and even pseudogenes\u2014the precise types of DNA which Francis Collins and others claim are non-functional \u201cgenetic flotsam and jetsam\u201d that demonstrate human\/ape common ancestry
\nCollins\u2019s argument from chromosomal fusion also fails to deliver. Even if a chromosomal fusion event occurred, it would tell us nothing about whether our lineage leads back to a common ancestor with apes. Of course, it isn\u2019t even completely clear that a chromosomal fusion has occurred. Interstitial telomeric DNA doesn\u2019t necessarily indicate a fusion event, and the interstitial telomeric sequences in human chromosome 2 are \u201chighly diverged\u201d from what we would expect from a recent fusion event.
\nAs a supporter of the idea that many aspects of nature are best explained by intelligent design rather than unguided processes, I want to note that intelligent design is not incompatible in principle with humans sharing ancestry with other species. At its core, intelligent design challenges not common ancestry, but the claim that life\u2019s complexity arose via unguided processes like random mutation and natural selection. Thus, a guided form of common ancestry would be compatible with intelligent design.
\nNevertheless, unlike proponents of Darwinian evolution, intelligent design theorists are not obligated to accept human\/ape common ancestry as a given. They are free to follow the evidence wherever it leads. And where the evidence leads is not to the conclusions promoted by Francis Collins. As we have seen, genetic arguments for human\/ape common ancestry are based more upon Darwinian assumptions and outdated data than careful deductions from the evidence.<\/p>\n
5<\/p>\n
THE SCIENCE OF ADAM AND EVE<\/p>\n
Ann Gauger<\/p>\n
Using population genetics, some scientists have argued that there is too much genetic diversity to have passed through a bottleneck of just two individuals. But that turns out not to be true.<\/p>\n
IN CHAPTER I, I ARGUED THAT OUR SIMILAR ANATOMY AND DNA sequences are not sufficient to demonstrate that we share a common ancestor with chimps. Using peer-reviewed scientific literature about transitional fossils, and what is known about current chimp and human anatomy, I concluded that there are too many anatomical changes and too little time for neo-Darwinian processes to have accomplished the supposed transition from our last common ancestor with chimps to us.
\nBut the current challenge concerning our origins involves more than fossils, anatomy, and improbable Darwinian scenarios. Now that DNA sequencing has become relatively simple and cheap, researchers are gathering vast amounts of human sequence data. They use the genetic variation they find to reconstruct past events in our genetic history. They derive evolutionary trees, estimate ancestral population sizes, and even calculate when and where our ancestors migrated out of Africa. Based on this kind of work, some have argued that we cannot have come from just two first parents.
\nThis argument directly contradicts the traditional belief of many Christians that humanity started with an original couple, Adam and Eve. Those affiliated with groups like the BioLogos Foundation have gone so far as to say that Christians must abandon a belief in Adam and Eve as sole parents of the human race, because scientific arguments supposedly have disproven the possibility of their existence.
\nNow, I am a scientist, and not a theologian, but I feel obligated to speak. The challenge being posed to two first parents is a scientific one, so it deserves a scientific response. My purpose in this chapter is not to engage in Biblical interpretation or to pass judgment on the various views Christians hold about Adam and Eve. Instead, I propose to focus on the scientific argument and its validity.
\nPopulation genetics arguments against Adam and Eve come in many forms. Here I will examine one of the strongest cases against a first couple\u2014the argument based on genetic variation in human leukocyte antigen (HLA) genes, some of the most variable genes in the human genome. When I began this study, I was prepared to accept that there was too much genetic diversity among these genes to have passed through just two first parents. To my surprise, I found that even this most polymorphic (most varied) region of our genome does not rule out the possibility of a first couple. And even more, buried within this region is evidence that suggests something more than common descent is responsible for our genetic make-up.
\nThe science here is complex. In order to critically assess the arguments being made, I have had to include a fair amount of technical discussion. I realize that parts of the chapter may be challenging to some readers, but I try to provide a clear statement of my major points in nontechnical language along the way.<\/p>\n
HLA GENES<\/p>\n
HLA GENES are involved in immune defense\u2014they bind and present foreign peptides on the surface of immune cells (leukocytes), in order to trigger a response by other immune cells. A number of these HLA genes are present in mammals, presumably to provide immunity against a wide variety of diseases and parasites. Figure 5-1 shows the location of the main HLA genes in humans.<\/p>\n
Figure 5-1: The human HLA genes.
\nIllustration: Ann Gauger (redrawn from a Wikipedia Commons illustration, public domain)<\/p>\n
There are many versions (alleles) currently known for each HLA gene. Because of this, the HLA complex represents one of the most difficult challenges to the idea that we came from just two first parents. If there are literally hundreds of alleles for these genes in the present human population, where did they come from? Two people can pass on at most four versions. Did all those alleles come from just two individuals with four or fewer ancestral versions?
\nTo answer that question, I need to explain something about the methods being used in these studies, and what their underlying assumptions are.<\/p>\n
WHAT IS POPULATION GENETICS?<\/p>\n
IN THE 1930s and 40s, Darwin\u2019s theory of evolution and Mendel\u2019s theory of genetics were combined, creating what is now called the Modern Synthesis, or what I prefer to call neo-Darwinism. Instead of focusing on how different animal forms might have evolved over time, neo-Darwinists began focusing on how genetic variation spread through populations. These \u201cpopulation geneticists,\u201d as they were called, developed mathematical models to extrapolate from existing genetic variation in populations to what may have happened to those populations in the past.
\nBecause all these models have their roots in Darwinism, they assume that natural selection acting on stochastic processes (processes that occur at random, and without consideration for the organism\u2019s needs) is sufficient to explain all evolutionary change. The stochastic processes that generate genetic variation include mutation (changes to the DNA sequence), and recombination (rearrangement or swapping of genetic information between chromosomes). Genetic drift (the stochastic loss of genetic information due to failure to reproduce) tends to reduce the power of natural selection to drive change, especially in populations of a million or less.
\nNote that for neo-Darwinism, there is no room for direction or guidance in evolution. Random genetic variation occurs by chance, without any provision for the organism\u2019s needs. Natural selection does the winnowing, and genetic drift throws in a dash of additional randomness as to which variants actually survive and spread through the population.
\nThe equations of population genetics require certain simplifications in order to make the mathematics work. Most models that use current genetic diversity to retroactively model past events assume a constant background mutation rate, with no strong selection biasing genetic change. They assume a constant population size with no migration in or out, and they assume that common descent is the underlying cause of sequence similarity. All these assumptions are subject to question, as we shall see.<\/p>\n
THE POPULATION GENETICS CHALLENGE TO TWO FIRST PARENTS<\/p>\n
IN THE 1990s a population biologist named Francisco Ayala set out to challenge the idea of two individual first parents, using sequence information from one of the HLA genes. Ayala chose HLA-DRB1 to make his point, because at that time there were already hundreds of different versions of HLA-DRB1 known. He had reason to suspect, therefore, that there might have been considerable diversity in HLA-DRB1 at the time chimp and human lineages supposedly diverged.<\/p>\n
Figure 5-2: Peptide-binding domain of HLA-DR.
\nIllustration: Ann Gauger, created using MacPymol and PDB 1aqd<\/p>\n
What does HLA-DRB1 do, and why is it so variable? The HLA-DRB1 protein combines with another protein called HLA-DRA to form a dimeric protein (seen above in Figure 5-2) called HLA-DR. (A dimer is a protein composed of two subunit proteins.) This protein dimer is embedded in the cell membrane of antigen presenting cells (a certain type of cell in the immune system). The dimer forms a peptide-binding pocket that binds foreign peptides, and presents them to other immune cells in order to trigger the production of appropriate antibodies.
\nThe reason why there are so many variants of HLA-DRB1 is that lots of variation in the peptide-binding pocket ensures that many different foreign peptides can be recognized and bound. This is a good thing because it strengthens immunity. If a new parasite or disease-causing microbe comes along, the chances are increased that some individual will have an allele of HLA-DRB1 able to bind the invaders\u2019 broken-up proteins, and trigger the immune system to mount a defense against them.
\nHere\u2019s the interesting thing. Nearly all the genetic variation in the HLA-DR dimer, and thus the variation in peptides that can be bound, comes specifically from just one portion of the HLA-DRB1 gene, namely exon 2. The rest of HLA-DRB1 or the HLA-DRA gene do not vary much.
\nAyala obtained chimp, human and macaque DNA sequences from just exon 2 of HLA-DRB1, and reconstructed the phylogenetic history of those sequences using population genetics algorithms. He drew an evolutionary tree that most closely fit the pattern of genetic variation in exon 2. Then using estimates from other sources for the average mutation rate, and the time that chimps and humans last shared a common ancestor, he calculated how far back on his tree that point of common ancestry was. Drawing a line across the tree at the point, he counted how many ancestral branches he crossed. That gave him an retrospective estimate of how many HLA-DRB1 alleles there must have been in the population at the time of the chimp\/human last common ancestor.
\nTo illustrate the basic process he followed, I have drawn a simple example of a phylogenetic gene tree (Figure 5-3). To the left is the oldest part of the tree. As time passes, the single gene duplicates and diverges, then splits again several more times. The final number of duplicates on the right is five (A\u2013E).<\/p>\n
Figure 5-3: Using phylogenetic trees to estimate lineages.
\nIllustration: Ann Gauger<\/p>\n
Normally population geneticists make the length of each horizontal line proportional to the amount of genetic change. The longer the length, the more nucleotide differences there are. Assuming the nucleotide differences are due to mutation over time, and assuming that mutations occur at a constant rate (not a sure thing, by the way), one can count backward to an estimated time in evolutionary history (in this case 50 and 250 years ago), and draw a line vertically through the tree. The number of lineages crossed by the line determine how many separate lineages were present at each particular time. If all estimates are correct, for this tree there would have been five lineages 50 years ago, and two lineages 250 years ago.
\nFollowing this procedure, Ayala calculated that there were thirty-two separate versions of the entire HLA-DRB1 gene present at the estimated time of our last common ancestor with chimps four to six million years ago (also not a sure thing\u2014these estimates keep changing). In order for all those variant alleles to make it to modern times, he further estimated that the minimum size of the ancestral population was no fewer than 4,000, with a long-term average effective population size of 100,000. This large number is necessary in a steady state population model like Ayala\u2019s. Under such conditions, assuming random mating and genetic drift, alleles are likely to be lost over time, so a large starting population is necessary to guarantee continued transmission of all the alleles. Because of this minimal estimate of 4,000, Ayala claimed that at no time was it possible for the human population to have passed through a bottleneck of two. In his view, there is just too much ancestral diversity in HLA-DRB1.<\/p>\n
THE CHALLENGE TO THE CHALLENGE<\/p>\n
LET\u2019S STEP back and examine how Ayala\u2019s analysis was done. His claims against a literal Adam and Eve are based on population genetics models for how gene frequencies change in populations over time, and how ancestral gene lineages tend to coalesce. The equations used to reconstruct these trees, and to calculate ancestral population sizes, depend on simplifications and assumptions to make the mathematics tractable, as I said before. These explicit assumptions include a constant background mutation rate over time, lack of selection for genetic change on the DNA sequences being studied, random breeding among individuals, no migrations in or out of the breeding population, and a constant population size. If any of these assumptions turn out to be unrealistic, the results of a model may be seriously flawed.
\nThere are also hidden assumptions buried in population genetics models, assumptions that rely upon the very thing they are meant to demonstrate. For example, tree-drawing algorithms assume that a tree of common descent exists. The population genetics equations also assume that random processes are the only causes of genetic change over time, an assumption drawn from naturalism. What if non-natural causes, or even unknown natural causes that do not act randomly, have intervened to produce genetic change?
\nIt turns out that the particular DNA sequence from HLA-DRB1 that Ayala used in his analysis was guaranteed to give an overestimate, because he inadequately controlled for two of the above assumptions\u2014the assumption that there is a lack of selection for genetic change on the DNA sequence being studied, and the assumption of a constant background mutation rate over time. HLA-DRB1 is known to be under strong selection for heterozygosity, meaning that having two different versions of the gene gives you a better chance of dealing with parasites and disease. Not only that, the particular region of the gene Ayala studied (exon 2) appears to have a mutation rate much higher than the background mutation rate. In fact, it is the most variable region of one of the most variable genes in our genome, and it may be a hotspot for gene conversion (a kind of mutation particularly likely to confuse assumptions of common descent and parsimony in tree-drawing), as we will see. Ayala did use a mathematical fudge factor for the first problem, but did not correct for the second problem.
\nA later study by Bergstr\u00f6m et al. examined the same HLA-DRB1 gene, but used intron 2, a portion of the gene not translated into protein. They chose the intron next to exon 2 expressly to avoid the confounding effects of strong selection, a high mutation rate, and\/or gene conversion. They verified that this intron had a mutation rate close to the genomic background. In contrast to Ayala\u2019s study, this study concluded that only seven versions of the gene existed in the ancestral population from which both chimps and humans supposedly came around 4\u20136 million years ago, and that the population had an estimated size of 10,000 rather than the 100,000 estimated by Ayala.
\nIn other words, by being careful about just two of the above assumptions, these researchers arrived at a dramatically lower estimate for the number of HLA-DRB1 alleles in the ancestral population than the number Ayala found in his study (i.e. seven alleles versus thirty-two). But the problems with Ayala\u2019s model go even deeper, as we shall see in the next section.<\/p>\n
PHYLOGENETIC CONFUSION<\/p>\n
AYALA CREATED his phylogenetic tree based on exon 2 sequences of the HLA-DRB1 genes, while Bergstr\u00f6m et al. used intron 2 sequences. A third study by Doxiadis et al. examined the phylogenetic histories of chimp, macaque and human HLA-DRB1 genes again, but this time using sequences taken either from exon 2 or introns 1-4. Surprisingly, the tree alignments using exon 2 or using introns 1-4 give markedly different pictures of the gene\u2019s phylogenetic history, even though both sets of sequences come from the very same genes. There is a substantial difference in the phylogenetic relationships. Exon 2 comparisons typically showed cross-species associations, while intron comparisons showed within-species associations.
\nA simplified illustration of the discordant phylogenetic trees is shown in Figure 5-4 below. (For the actual trees, see Doxiadis et al.) It is clear that the intron sequences group according to species, whereas exon 2 sequences show no species-dependent relationships.<\/p>\n
Figure 5-4: Discordant intron-and exon-based phylogenetic trees.
\nIllustration: Ann Gauger<\/p>\n
This should be surprising. Although trees based on gene comparisons sometimes do not show the same phylogenetic relationships as the species themselves do, as is the case for the exon 2 sequences, when this happens it indicates something unusual is going on.
\nIt\u2019s even more unusual that trees drawn from adjacent segments of the same gene disagree with one another. It\u2019s not that exon 2 is highly variable and the introns are more conserved, because this is not the case. Intron lineages can differ quite a bit from one another. Rather, the intron lineages group together according to species, while the exon 2 lineages do not.
\nSome evolutionary biologists try to explain this discordance between the HLA-DRB1 trees by arguing that this proves that these genes have their origin in deep time, before the lineages of chimps, humans and macaques separated, and that it is the exon 2 data that defines the gene\u2019s history. Others think that there has been cross-species shuffling of ancient peptide-binding motifs between different exon 2 sequences over time, but leaving the intron lineages unchanged. It is not clear, however, how such a patchwork cross-species assortment of exon 2 sequences could have been acquired without disrupting the species-specific introns. Furthermore, this would require that the incipient species\u2019 populations intermingled for a prolonged period of time. The intermingling is highly unlikely to have lasted for thirty million years, though, which is the last time macaques, chimps, and humans supposedly shared a common ancestor. And the fact that the intron sequences do associate by species, with branch lengths as long or longer than the exon branch lengths, argues that many of these intronic lineages have been evolving independently for quite a while, indeed some as long as thirty to forty million years. Therefore this phylogenetic discordance is something that cannot be explained by common ancestry, especially when one considers an additional piece of information: The HLA-DRB1 region of chromosome six shows little or no signs of recombination.<\/p>\n
SPECIAL BEHAVIOR, SPECIAL DESIGN?<\/p>\n
HLA-DRBI\u2019S CLOSEST neighbors, HLA-DQB and HLA-DQA, also bind and present foreign peptides to other immune cells, like HLADRB1. According to Raymond et al., this region shows extreme linkage disequilibrium, meaning that there is little or no reciprocal recombination between these genes.
\nThis lack of recombination is highly unusual because it extends over 80,000 bases of DNA. Stretches of DNA that do not undergo genetic recombination are called haplotypes. Normally, given the supposed age of these haplotypes, recombination should have occurred roughly every 150 nucleotides. Recombination does take place elsewhere in the region, just not in the vicinity of HLA-DRB1.
\nDespite the fact that there are hundreds of alleles for each HLA gene, only certain combinations of alleles of HLA-DQ and HLA-DR tend to occur together\u2014they are inherited as a block. It may be that particular combinations of alleles work especially well together, while other less favorable combinations are removed from the population by natural selection. Alternatively, recombination may be suppressed by some other mechanism.
\nThese co-inherited combinations of alleles constitute the basic haplotypes of HLA-DRB1. Most researchers now agree that there are just five of these basic haplotypes in humans. Which HLA-DRB1 gene a particular haplotype has tends to specify the particular allelic combinations of other genes in the haplotype. Based on the amount of background genetic change in the introns, three haplotypes appear to be ancient, going back thirty million years or more. These are the haplotypes we have in common with chimps and macaques. Two haplotypes are more recent, based on their accumulated background mutation, and date back to about four to six million years ago. Thus, depending on when one places the time of the proposed divergence, there may have been as few as three ancestral haplotypes, or as many as five, when hominins diverged.<\/p>\n
TAKE HOME MESSAGE<\/p>\n
HERE is the whole point in simple language. The argument from population genetics has been that there is too much genetic diversity to pass through a bottleneck of two individuals, as would be the case for Adam and Eve. But that turns out not to be true.
\nIn fact, when all the data are considered, there are just five basic versions of the HLA haplotype. Three appear to be ancient, pre-dating any supposed evolutionary split between chimps and humans, and two are more recent (some time before or after the putative most recent common ancestor of primates and humans, depending on where you draw the line). At least one of these five haplotypes appears to be missing in chimps. Given the difficulties involved in estimating the times of divergence due to the unusual genetic behavior of the region, it is possible that four or fewer of those haplotypes pre-date our supposed divergence from chimps.
\nEach person carries two copies of the Class II haplotype, so each person can carry two different alleles of HLA-DRB1. Therefore, those four haplotypes could potentially be carried by just two individuals. This means that a first couple could have carried sufficient genetic diversity to account for four basic haplotypes, especially given the possibility of rapid population expansion afterward.
\nWe have dropped from an estimated 32 lineages based on DRB1 exon 2 comparisons, to seven lineages using DRB1 intron 2 comparisons, and then to between three and five ancestral haplotypes, when the whole region is considered. This is a remarkable reversal. What once seemed to be a rock-solid argument against the existence of a first couple has now dwindled considerably. The genetic analysis indicates that a first couple is possible. At the very least it is fair to say that HLA haplotype diversity cannot rule out two first parents.
\nWhat about the problem of genetic drift, and the concomitant need for a large population to prevent loss of variant haplotypes? That problem applies for a steady state, constant-size population model, but not in the case where rapid population growth is taking place. In the case of a newly emerging (created) species, rapid expansion would make it possible for all haplotypes to be preserved. In fact, there is evidence that HLA diversity increases rapidly after a new population is founded, though not usually to this degree.
\nNow I would like to move in a more challenging direction. What if our sequence similarities are not the result of common descent? What if we began from two intelligently designed first parents? Is there any evidence in the data I have presented to indicate that this might be the case? If so, all this analysis of how many ancient haplotypes we share with chimps doesn\u2019t really matter.
\nThere certainly are surprising patterns of genetic variation within HLA-DRB1 that suggest unknown processes may be operating. Let me propose that a process exists which generates specific hypervariability within exon 2 and suppresses recombination elsewhere. The process is targeted to generate diversity precisely in the peptide-binding domain. I suggest that intelligent design had to be involved at the beginning, in order to rapidly generate HLA diversity after the foundation of our new species (assuming we came from two first parents). Evidence supporting this idea comes from the fact that HLA-DRB1 diversity has in fact increased very rapidly by anyone\u2019s count, going from a handful of variants to over six hundred alleles in six million years or less. Also, the HLA-DRB1 variable regions in exon 2 show a patchwork, cross-species relationship to their surrounding DNA sequences, making their origin hard to account for by common descent. Their repeated use of similar motifs from different species may instead indicate common design. I further suggest that this process may be human-specific, since other primates don\u2019t show nearly the same degree of allelic diversity within lineages as humans do.
\nThis proposal can be supported at least in part by published data. Both gene conversion and hypermutation are known to generate antibody diversity in other immune cell lineages. Sequence analysis of HLA-DRB1 alleles reveal that \u201crecombination events either strictly located at exon 2 or involving adjacent introns have occurred\u201d and \u201cindicate that interlineage recombinations may be hidden and are perhaps more frequent than currently expected.\u201d Others have identified sequence features thought to be involved in recombination processes, some of which are highly conserved across HLA-DRB1 alleles.
\nIn addition, several human population studies indicate that many HLA Class I and Class II genes undergo rapid interallelic recombination. For example Hedrick and Kim report that:<\/p>\n
new alleles that appear to be the result of microrecombination between other alleles have been found in South American Amerindians and other populations. Because the Americas have probably been populated for only the last 10,000 to 20,000 years (~ 1000 human generations), the new variants, which do not appear in Asian samples, must have arisen in this period.<\/p>\n
These include several novel variants in HLA-DRB1, HLA-DPB1, and HLA-B. Hedrick and Kim go on to say:<\/p>\n
there is direct evidence that the rate of microrecombination at some MHC loci is high.\u2026 Zangenberg et al. (1995) examined the rate of interallelic gene conversion at the HLA-DPB1 locus in sperm from males heterozygous for six regions of the highly variable exon 2. In 111,675 sperm, they observed nine interallelic conversions for a rate of 0.81 \u00d7 10\u22123, nearly 1 in 10,000 gametes.<\/p>\n
Given this data, it seems not unreasonable to propose that HLA-DRB1 diversity is the result of a process that generates specific hypervariability and\/or gene conversion within exon 2 in order to rapidly generate HLA diversity. The existence of such a process essentially demolishes any population genetics arguments about ancestral population sizes.
\nThe HLA story illustrates well the strengths and the limitations of science. Scientific claims are provisional, always subject to revision. In particular, retrospective calculations should be treated with caution, because of the number of unknown variables and hidden assumptions involved. Where ancient genetic history is involved, dogmatic statements are out of place. We understand very little of our own genetic makeup\u2014way too little to make accurate calculations about our distant genetic past. But there are still plenty of interesting things to discover, and new proposals to consider.<\/p>\n
RECONSIDERING THE EVOLUTIONARY STORY<\/p>\n
I CHOSE to look at the HLA-DRB1 story because it seemed to provide the strongest case from population genetics against two first parents. If it were true that we share thirty-two separate lineages of HLA-DRB1 with chimps, it would indeed cause difficulties for an original couple. But as we have seen, the data indicate that it is possible for us to have come from just two first parents.
\nMoreover, the data indicate that DNA similarity is not going to be a simple story to unravel. There are already regions of human DNA known to more closely resemble gorilla sequences than chimp sequences. Now we have sequences that resemble macaque DNA, a primate not part of the hominid group. Furthermore, when adjacent regions of DNA yield different evolutionary trees, linked to species that diverged well before the putative most recent common ancestor of chimps and humans, something unusual is going on.
\nThis result was a surprise to me, and threw me back into a consideration of the whole story of our common descent from ape-like ancestors. I already knew from my own research that similarity of form or structure was not enough to demonstrate that neo-Darwinian common descent was possible. I knew that genuine protein innovations were beyond the reach of naturalistic processes. I therefore began to re-examine everything I knew or thought I knew about human origins. I reviewed paleoanthropology, evolutionary psychology and population genetics research articles, I reviewed popular books and textbooks. I applied strict logic to the story of what would be required for our evolution from great apes. As a result of all this reading and reflection, although I was always skeptical about the plausibility of human evolution by neo-Darwinian means, I have now come to wonder about the extent of common descent as well.
\nCurrently, neo-Darwinism is the accepted explanation for our origin. It may be, though, that as we continue to investigate our own genomes, the Darwinian explanation for our similarity with chimps\u2014namely, common descent\u2014will evaporate. We may discover additional features in our genome that defy explanation based on common ancestry. As evidence of common descent\u2019s insufficiency as a theory grows, alternate theories will need to be tested.
\nBut one thing is clear right now: Adam and Eve have not been disproven by science, and those who claim otherwise are misrepresenting the scientific evidence.<\/p>\n","protected":false},"excerpt":{"rendered":"
SCIENCE AND HUMAN ORIGINS ANN GAUGER DOUGLAS AXE CASEY LUSKIN SEATTLE DISCOVERY INSTITUTE PRESS 2012 Description Evidence for a purely Darwinian account of human origins is supposed to be overwhelming. But is it? In this provocative book, three scientists challenge the claim that undirected natural selection is capable of building a human being, critically assess … <\/p>\n