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Rethinking Human Evolution
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Volume 52 Number 4, July/August 1999
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by Ian Tattersall
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The immediate postwar period was an important one for the field of paleoanthropology, less for discoveries of new fossils than because this was the time when the discipline absorbed the theoretical underpinnings that continue to influence it to the present day. The years leading up to World War II had seen the emergence of the evolutionary synthesis, a body of theory that swept away a host of conflicting notions about the nature of the evolutionary process, replacing them with the elegantly simple concept that all evolutionary phenomena could be ascribed to a single mechanism: the gradual change of genes and gene frequencies within lineages of organisms under the guiding hand of natural selection. The principal architects of the synthesis, notably the geneticist Theodosius Dobzhansky and the ornithologist Ernst Mayr, were happy to share their insight with their paleoanthropological colleagues, and in the years around 1950 they played a powerful role in reshaping the field of human evolution.
Fifty years ago the human fossil record was fairly sparse, and the dating of known specimens was limited to "older than/younger than" statements with a strong dose of uncertainty. The hominid status of the australopithecines (small-brained early bipeds) was already largely established, and it was known that Homo erectus, in the guise of Java Man and Peking Man, lay somehow intermediate between these early forms and the later Neandertals, a group already abundantly known from late Ice Age sites in Europe and western Asia. But the picture was still complicated by the specter of the Piltdown "fossil," an allegedly ancient, large-brained hominid whose fraudulence was proved only in 1953. There was also a plethora of species and genus names, applied liberally and capriciously to hominid fossils from around the Old World, that hampered attempts to make sense of the known record.
Little wonder that in this confusion paleoanthropologists welcomed Dobzhansky and Mayr's simplifying messages. Dobzhansky announced his view that only one kind of hominid could have existed at any time and that virtually all developments in human evolution since Java Man had taken place within the single, albeit variable, species Homo sapiens. Mayr touted the notion that at most three successive species could be discerned within the genus Homo: H. transvaalensis (the australopithecines), H. erectus, and H. sapiens (including the Neandertals). While few paleoanthropologists followed these pronouncements in all their details, schemas of hominid evolution routinely came to incorporate the synthesis' basic assumptions, whereby evolutionary change consisted simply of the gradual modification of lineages, usually no more than one, over long spans of time. Human evolution thus became the story of a long, single-minded struggle from primitiveness to perfection.
Fifty years later, our perspective on human evolution has changed beyond recognition. For one thing, we have made remarkable progress in our understanding of the evolutionary process, and in ways of analyzing the fossil record. And for another, the hominid fossil record itself has expanded wonderfully, as has the archaeological record that accompanies it. What all of these discoveries have made clear is that, far from having been a single-minded linear struggle, a matter of constantly perfecting adaptation, the history of the hominid family has been one of repeated evolutionary trial and error: of new hominid species spawned, competing, and becoming extinct. We take it for granted that Homo sapiens is the lone hominid on Earth, but this is probably unusual. In the past, coexistence and competition among hominid species have quite likely been much more typical. This realization is salutary, for whereas our egotistical species likes to think of itself as the pinnacle of evolution, any accurate view of ourselves requires recognizing Homo sapiens as merely one more twig on a great branching bush of evolutionary experimentation.
Ian Tattersall, the author of numerous books including the recently released Becoming Human, is a curator of anthropology at the American Museum of Natural History.
© 1999 by the Archaeological Institute of America
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