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September 11, 2006
Part I: What Makes Us Human?
Chimpanzee Comparative Genomics
Andrew Clark
Cornell University
37 min. (slideshow requires QCShow Player)
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The long hours spent with [the chimpanzees] in the forest have enriched my life beyond measure. What I have learned from them has shaped my understanding of human behavior, of our place in nature.
— Jane Goodall
The answer to the question: What makes us human? is greatly confused by the two dichotomous views we maintain of ourselves. On one hand, we now know that we share more than 98% of our genes with chimpanzees. On the other, we see ourselves as fundamentally different beings, possessing an intelligence and a spirit we don't see in the chimps. If nothing else, we are a uniquely religious animal. We are wholly aware of our own impending deaths.
Julian Huxley created the words clade and grade to represent the two features of evolution that he believed were self-evident. Cladistics has now become a well established part of the scientific enterprise. But the term "grade" has essentially disappeared from the biologist's lexicon, if only temporarily, simply because the notion of evolution as a progressive process has been so deprecated in recent years.
In Huxley's view, clades are defined by common ancestry while grades are representative of profound evolutionary advances onto new plateaus. In his book, New Bottles for New Wine (1957), he wrote:
"I personally would like to see a new evolutionary classification, which would combine the advance and ancestry principles. We would have groups (or 'clades,' from the Greek for branches) of common ancestry — and grades of advance for which new designations would be needed... I would hope that Metazoa would be restored to its original use as a grade label and that Man would be placed in a new major grade, which might be called Psychozoa."
In recent years, chimpanzees, gorillas and orangutans have been assigned to the Family Hominidae, once the exclusive province of humans. We clearly belong together. But we are different too, currently the sole member of the grade Psychozoa. If there is to be another species in this grade, the greatest probability will be that it's one we build ourselves mechanically, a self-aware, conscious being capable of exploring the galaxy in a manner that we can't. As Seth Shostak commented in an earlier lecture, "Biological intelligence, as interesting as it is, may only be a cheap motel on the way to true galactic intelligence."
During that time when gene sequencing was a new enterprise, requiring hundreds of people working on a single protein for a year or more, some of the first investigations into sequencing were done to determine what form of differences exist between chimpanzee and human. For the first half-dozen or so proteins sequenced, which were reported over an equal number of years, no differences were found, leading one wag to say that "when we're finished with this, the only differences between the chimpanzee and us will be found to be cultural."
But if we are as different from the other apes as we believe ourselves to be, then those differences should be reflected in our genetics. The technology of gene sequencing has seen extraordinary advances recently, and in this lecture, Andrew Clark presents the results of the most comprehensive gene-comparison project to date.
The differences found are not what anyone predicted. The most "accelerated" genes in the evolution of hominids appear in those genes associated with hearing, signal transduction, amino acid catabolism, long-bone growth and hairiness, but not in brain function or architecture, the attributes of our humanity for which we most pride ourselves.
Post hoc explanations can be created for each of these observed differences, but post hoc explanations always tread dangerously to "Just-So" stories. Nevertheless, they're often all we have, and Clark more reasonably describes them as "hypothesis generators."
Accelerated changes in amino acid catabolisms can be reasonably explained by the rapid shifts in ecology that the hominid lineage underwent following its split from the arboreal apes. Similarly, changes in signal transduction and hearing architectures can likely be explained not only by the change in sensory environment associated with an upright gait but also by the necessity of increased oral acuity accompanying the evolution of language. The difficulties in training chimps to understand speech may well be attributable to the inadequate mechanics of their hearing apparatus. Changes in the genetics of long-bone growth and hairiness seem more obvious yet.
Nonetheless, even if these explanations are true, where is the "gene" for our self-awareness? To ask that question misunderstands the nature of complex systems design. The question is akin to asking which piece, in the thousands of pieces that go into the construction of a jetliner, determines its flight efficiency? The quality of flight efficiency doesn't exist in any single rivet or piece of sheet metal, but rather it pervades all of them. Flight efficiency comes into existence only after they have been integrated into a working whole. Self-awareness, intelligence and religiousity are similar qualities and are undoubtedly so pervasive to our architecture that they may always be below our technical capacity to find them at any level of statistical significance.
— Wirt Atmar
About the Speaker
Dr. Andrew G. Clark is Professor of Population Genetics in the Department of Molecular Biology and Genetics. He received a B.S. in Biology and Applied Mathematics at Brown University in 1976, and a Ph.D. in Population Genetics at Stanford University in 1980. He did postdoctoral work at Arizona State University and the University of Aarhus, Denmark, and a sabbatical at the University of California at Davis. Prior to joining the Cornell faculty in 2002, he was a professor in the Department of Biology at Penn State University.
Dr. Clark's research focuses on the genetic basis of adaptive variation in natural populations, with emphasis on quantitative modeling of phenotypes as networks of interacting genes. Dr. Clark has been active in genomics research and has been a frequent consultant with Celera Genomics since April 1999. He was elected Fellow of the American Association for the Advancement of Science in 1994, and serves on review panels for the NIH, NSF, and the Max Planck Society. Dr. Clark's research has been supported by the National Institutes of Health, the National Science Foundation, the Alfred P. Sloan Foundation, NATO, and the Marsden Fund.
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