Allan Wilson - Career and Scientific Contributions

Career and Scientific Contributions

Wilson's first major scientific contribution was published as Immunological Time-Scale For Hominid Evolution in the journal Science in December 1967. Wilson and has Ph.D. student Vincent Sarich showed evidence that evolutionary relationships of the human species with other Primates, in particular the Great Apes, (Chimpanzees, Gorillas, and Orangutans) could be inferred from molecular evidence taken from living species, rather than solely from fossils of extinct creatures. Their microcomplement fixation method measured the strength of the immunological reaction between an antigen (serum albumin) from one species and an antibody raised against the same antigen in another species. The strength of the antibody-antigen reaction was known to stronger between more closely related species: their innovation was to measure it quantitatively among many species pairs as an "immunological distance". When calibrated against known divergence times between certain species pairs, they showed that the molecular difference increased linearly with time, in what was termed a "molecular clock". Given the calibration curve, the time of divergence between species pairs with unknown or uncertain fossil histories could be inferred. The data of Wilson and Sarich suggested that divergences between humans, chimpanzees, and gorillas were on the order of 3 ~ 5 million years, far less than the estimates of 9 ~ 30 million years by conventional "paleoanthropologists" from fossil hominids such as ''Ramapithecus''. This 'recent origin' theory of human /; ape divergence remained controversial until the discovery of the ""]" fossils in 1974.

Wilson and another Ph.D. student Mary-Claire King, subsequently compared several lines of genetic evidence (immunology, amino acid differences, and protein electrophoresis) on the divergence of humans and chimpanzees, and showed that all methods agreed that the two species were more than 99 percent similar. Given the large organismal differences between the two species in the absence of large genetic differences, King and Wilson argued that is was not structural gene differences that were responsible for species differences, but gene regulation of those differences, that is, the timing and manner in which near-identical gene products are assembled during embryology and development.

In the early 1980s, Wilson further refined traditional anthropological thinking with his work with Ph.D. students Rebecca Cann and Mark Stoneking on the so-called "Mitochondrial Eve" hypothesis. In his efforts to identify informative genetic markers for tracking human evolutionary history, he started to focus on mitochondrial DNA (mtDNA) — genes that are found in mitochondria in the cytoplasm of the cell outside the nucleus. Because of its location in the cytoplasm, mtDNA is passed exclusively from mother to child, the father making no contribution. Because it also mutates rapidly, it is possible to measure the small genetic differences between individual within species by restriction endonuclease gene mapping. Wilson, Cann, and Stoneking measured differences among many individuals from different human continental groups, and found that humans from Africa showed the greatest inter-individual differences, consistent with an African origin of the human species (the so-called "''Out of Africa''" hypothesis). The data further indicated that all living humans shared a common maternal ancestor, who lived in Africa only a few hundreds of thousands of years ago. This common ancestor became widely known in the media and popular culture as the "Mitochondrial Eve". The erroneous implication was that only a single female lived at that time, when in fact the occurrence of a coalescent ancestor is a necessary consequence of population genetic theory, and the "mitochondrial Eve" was only one of many humans (male and female) alive at that time.

This finding was, like his earlier results, not immediately accepted by anthropologists. Accepted thinking had various human groups evolving from different ancestors, over a million years in separate geographic regions, but at basically the same rate around the world. Subsequent investigation by direct DNA sequencing of mitochondrial DNA as well as nuclear DNA