When many people hear about the controversy over human origins, they usually think of creation versus evolution. However, some of the most heated debates occur within the theory of evolution itself. According to the November 3, 2007, issue of the journal Science News, 'Given limited evidence about long-gone populations of our predecessors, researchers devise competing evolutionary scenarios that are often difficult to disprove and that can easily accommodate whatever ancient bones turn up next' (Bower 2007: 280).
An example of this takes the form of an ancient braincase and partial upper jaw unearthed in Kenya in 2000. The discoverers claim that these two fossils prove that there were two species of Homo (the genus that includes modern humans) that lived at the same time in East Africa between 1.9 million and 1.4 million year ago. However, as Science News reports, 'one prominent anthropologist rejects that conclusion, placing both new fossils in a single species that preceded Homo sapiens'-that is, modern humans (Ibid.).
Standard evolutionary theory maintains that Homo habilis, a small-brained primate that is believed to have evolved about 2 million years ago from earlier primates in East Africa, evolved into the larger-brained Homo erectus about 1.6 million years ago, and that Homo erectus evolved into us. After teaching this as dogma for decades, some scientists are beginning to doubt this scenario. Anatomist Fred Spoor of University College London and his colleagues maintain that H. habilis and H. erectus evolved separately, and lived side by side in East Africa for half a million years (Ibid. 282).
They base their conclusion on the two fossil finds mentioned above. The first is a piece of upper jaw, which was found in a layer of volcanic ash dated under current assumptions to 1.44 million years ago. The jaw, which still contains six teeth, belongs to H. habilis, according to Spoor. The second find is a small braincase whose age is estimated at 1.55 million years, and 'bears several traits unique to H. erectus,' according to Science News (Ibid.).
The journal further points out: 'Since the two species coexisted in the same region for such a long time, each must have had separate origins between 3 million and 2 million years ago, [Spoor and his colleagues] contend. Few hominid fossils have turned up from that period' (Ibid.). Spoor concludes that modern humans evolved from H. erectus, possibly via an intermediate species as yet unknown, while H. habilis was a 'sister species' of H. erectus that eventually reached an evolutionary dead end (Ibid.).
Not all scientists agree. Tim White of the University of California, Berkeley, one of the leading anthropologists of all time, has classified both fossils as H. erectus and as important contributions to the study or origins, 'but hardly the stuff of major evolutionary revisions,' in the words of Science News (Ibid.). He rejects Spoor's image of the human evolutionary line branching out into multiple species, maintaining instead the standard, familiar model of early hominids evolving in a straight line (Ibid.).
This controversy demonstrates the high degree of uncertainty that surrounds the search for human origins. Despite the fact that the popular image of ape-to-hominid-to-man is presented as all-but-irrefutable fact, the truth is not so well known, and everything we know about the origin of the human race could change at any moment with any new discovery.
Bower, B. 2007. 'Fossil Sparks.' Science News 172, no. 18.