Who WAS Homo habilis?

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June 17, 2011

A summary article in Science this week asks this question, after revealing the results of another study of ancient eating habits, and in general revisits the many questions connected with this much debated ancestor. Two weeks ago researchers reported (see News in BecomingHuman.org) their analysis of isotopic Strontium indicated the females of Australopithecus taxa from about 2 million years ago in South Africa ranged more widely than their males and an analysis published in the Proceedings of the National Academy of Sciences this week says tooth wear analysis indicates the diet of Homo habilis was more like that of Australopithecus than later Homo.

Fossils found at Olduvai Gorge in 1964 by Louis Leakey were said by him to be evidence of the earliest member of the Homo lineage and named Homo habilis (“handy man”) because they were found in the same general area as stone tools. H. habilis was small statured, unlike later finds of H. erectus and when more examples of Australopithecus were found in subsequent decades, it was clear the brain size of H. habilis was only slightly larger than that of contemporary australopithecines.

Science writer Ann Gibbons summarizes these questions and provides a good opportunity not only to read her article in Science but also visit the Homo habilis essay elsewhere on this website and become reacquainted with these questions.

It is fair to say the phylogenetic placement and taxonomic assignment of H. habilis will remain open to debate for a very long time for, as Dr. Bernard Wood has suggested, it is equally difficult to assign these fossils to Australopithecus or Homo. H. habilis will continue to be ambiguous.

The author of the article discussed above, Ann Gibbons, moderates a live chat each Thursday from the Science Live site. On June 23, 2011 Gibbons' topic was "Who was the first human" and scientists Bill Kimbel, Director of the Institute of Human Origins at Arizona State University and Peter Ungar, chair of the Department of Anthropology at the University of Arkansas took questions typed online by live chat guests.  By clicking here you can go to the Science Live site and read the entire June 23rd session.  Bill Kimbel's opening statement introduces the subject.  He said,

The answer to the question “Who were the first humans?” depends on what we mean by “human.” If we mean the earliest representatives of Homo, the genus to which we belong, then the answer is quite different from the one if we mean the earliest people whose anatomy closely resembles our own (so-called anatomically modern Homo sapiens). The problem is due to the fact that the evolutionary lineage leading to us has been characterized by a great deal of cumulative change in anatomical and behavioral traits over more than 2 million years — and so, to a certain extent, what we call “human” is arbitrary in that it depends on which traits we choose to focus on. Brain enlargement? Body proportions? A certain degree of technological skill (e.g., hunting)? Language and other traces of symbolic behavior? Each of these will yield a different answer to the question because they did not evolve together in lock-step fashion. The point is, there is no set of privileged traits that defines “human,” simply because humans have evolved.

Later, in answer to the question what was for you the most interesting portion of the hominin fossil record, Kimbel said,

The thing that I find most interesting about the hominin fossil record is the diversity of adaptations that evolved to meet the challenges of changing environments after 3.0 myr. Although the record is imperfect, we can i think see the traces of a radiation of species with new adaptations to drier, more seasonal environments. It's an adaptive radiation, similar to that of the Galapagos finches, for example. I think in many ways the fossil record between 2 and 3 myr is the most excioting from this perspecitve.