Pygmy chimpanzee as a possible prototype for the common ancestor of humans, chimpanzees and gorillas

Abstract

A CONVINCING theory of human origins must clarify man's relationships with living primates and with the ancestral forms known only through fossils. Phylogenetic relationships have previously been determined mainly by anatomical similarities, but now, biochemical similarities provide independent criteria for evolutionary relationships. Albumin and transferrin immunology, immunodifrusion, DNA annealing and amino acid analysis all indicate that chimpanzees, gorillas and humans share a substantial common ancestry, and that the Asiatic apes (gibbons and orangutans) diverged earlier from this lineage^1–3. These findings directly conflict with the more widely held view that all the great apes diverged from a common ancestor long after the ‘Origin’ of the evolutionary line leading to modern humans⁴. The molecular data consistently suggest a much more recent origin of the man–chimpanzee–gorilla separation than was previously imagined, namely, in the range of 4–6 M yr ago^3,5. These data show that, although the two chimpanzee species (Pan paniscus and P. troglodytes) are biochemically distinct, they are more closely related to each other than either is to humans or gorillas^6,7. The chimpanzees speciated, then, after the initial three-way split. We therefore, here contend that, among living species, the pygmy chimpanzee (P. paniscus) offers us the best prototype of the prehominid ancestor. Biochemical, morphological, behavioural and palaeontological data support this proposition and argue for a relatively recent and accelerated divergence of the hominid from the pongid line.