The Origin of Humankind Read Free Page B

were ancient, as were those yielding subsequent similiar discoveries in Asia and Africa. Simons and Pilbeam therefore concluded that the first humans appeared at least 15 million years ago, and possibly 30 million years ago, and this view was accepted by the vast majority of anthropologists. Moreover, the belief in so ancient an origin placed a comforting distance between humans and the rest of nature, which many welcomed.
    In the late 1960s, two biochemists at the University of California, Berkeley, Allan Wilson and Vincent Sarich, came to a very different conclusion about when the first human species evolved. Instead of working with fossils, they compared the structure of certain blood proteins from living humans and African apes. Their aim was to determine the degree of structural difference between human and ape proteins—a difference that should increase at a calculable rate with time, as a result of mutation. The longer humans and apes had been separate species, the greater the number of mutations that would have accumulated. Wilson and Sarich calculated the mutation rate and were therefore able to use their blood-protein data as a molecular clock.
    According to the clock, the first human species evolved only about 5 million years ago, a finding that was dramatically at variance with the 15 to 30 million years of prevailing anthropological theory. Wilson and Sarich’s data also indicated that the blood proteins of humans, chimpanzees, and gorillas are equally different from each other. In other words, some kind of evolutionary event 5 million years ago caused a common ancestor to split in three directions simultaneously—a split that led to the evolution not only of modern humans but of modern chimpanzees and modern gorillas. This, too, was contrary to what most anthropologists believed. According to conventional wisdom, chimpanzees and gorillas are each other’s closest relatives, with humans standing a great distance apart. If the interpretation of the molecular data was valid, then anthropologists would have to accept a much closer biological relationship between humans and apes than most believed.
    An almighty dispute erupted, with anthropologists and biochemists criticizing each other’s professional techniques in the strongest of language. Wilson and Sarich’s conclusion was criticized on the ground, among others, that their molecular clock was erratic and therefore could not be relied upon to give an accurate time for past evolutionary events. Wilson and Sarich, for their part, argued that anthropologists placed too much interpretive weight on small, fragmentary anatomical features, and were thus led to invalid conclusions. I sided with the anthropological community at the time, believing Wilson and Sarich to be incorrect.
    The debate raged for more than a decade, during which time more and more molecular evidence was produced—by Wilson and Sarich and also independently by other researchers. The great majority of these new data supported Wilson and Sarich’s original contention. The weight of this evidence began to shift anthropological opinion, but the change was slow. Finally, in the early 1980s, discoveries of much more complete specimens of Ramapithecus-like fossils, by Pilbeam and his team in Pakistan and by Peter Andrews, of London’s Natural History Museum, and his colleagues in Turkey, settled the issue (see figure 1.1 ).
    The original Ramapithecus fossils are indeed humanlike in some ways, but the species was not human. The task of inferring an evolutionary link based on extremely fragmentary evidence is more difficult than most people realize, and there are many traps for the unwary. Simons and Pilbeam had been ensnared in one of those traps: anatomical similarity does not unequivocally imply evolutionary relatedness. The more complete specimens from Pakistan and Turkey revealed that the putative humanlike features were superficial. The jaw of Ramapithecus was V-shaped, not an arch; this and