The last decade has witnessed three contenders for the title: earliest identifiable human ancestor. These are Ardipithecus, Orrorin and Sahelanthropus. All of them generated great excitement at the time of their discovery and, for many, they were evidence that the lineage of the human genus was being clarified. However, those willing to read research papers (rather than media reports) were more aware that the research community was not of one mind about the significance of these fossil remains. Recently, Wood and Harrison have contributed a major review paper that revisits these arguments and finds that the various claims for human ancestry are not rigorous. They offer alternative explanations for these three fossil hominines.
“In their paper, Wood and Harrison caution that history has shown how uncritical reliance on a few similarities between fossil apes and humans can lead to incorrect assumptions about evolutionary relationships. They point to the case of Ramapithecus, a species of fossil ape from south Asia, which was mistakenly assumed to be an early human ancestor in the 1960s and 1970s, but later found to be a close relative of the orangutan.”
The key arguments are presented in a section of their paper entitled: “Shared morphology need not mean shared history”. They refer, in particular, to three anatomical characteristics. The first is concerned with canine morphology, the second with the location and orientation of the foramen magnum, and the third with features of the pelvis and other bones that have implications for bipedalism. These character traits have been prominent in discussions of the significance of Ardipithecus, Orrorin and Sahelanthropus. The problem identified by Wood and Harrison is homoplasy, where the same biological trait appears in unrelated lineages. Homoplasy leads to false homologies.
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