Born in Africa_ The Quest for the Origins of Human Life - Martin Meredith [51]
All this required some new thinking about human evolution. The common view at the time of Lucy’s discovery was that upright walking had evolved from the need by proto-humans to free their hands to make tools and to carry them and other objects around. But afarensis showed that hominids walked upright as much as a million years before stone tools appeared in the archaeological record. A new theory was needed, therefore, to explain why human ancestors walked upright in the first place.
While palaeoanthropologists were preoccupied with the business of fossils, other scientists began to make increasing inroads into what they regarded as their domain, provoking a new set of arguments. At the forefront was a group of biochemists and molecular biologists who argued that molecular evidence was more reliable than morphological evidence in uncovering evolutionary histories. In 1962, Emile Zuckerkandl and Linus Pauling, two pioneering scientists at the California Institute of Technology, used the term ‘molecular anthropology’ to describe this new field of research. Their work showed that the structure of molecules of blood proteins—specifically haemoglobin—changed over time with such regularity that it provided a molecular ‘clock’ that could be used to help construct evolutionary, or phylogenetic, trees. In a paper published in 1965, they referred to molecules as ‘documents of evolutionary history’.
They were followed by Morris Goodman, a biochemist at Wayne State University’s School of Medicine in Detroit, who produced a phylogenetic tree based on immunological data that challenged accepted notions about the evolutionary relationship between great apes and humans. Hitherto, zoologists had classified the great apes under one family, the Pongidae, while placing humans in their own family, the Hominidae. Goodman’s tests on blood proteins showed that African apes—chimpanzees and gorillas—were more closely related to humans than were Asian apes—orang-utans and gibbons. And he proposed that because of their genetic propinquity, humans, chimpanzees and gorillas should be placed in the same family. Furthermore, his tree showed that humans, gorillas and chimpanzees had split from a common ancestor at a similar period of time; the conventional view was that humans had separated at a much earlier time.
In the late 1960s, two Berkeley biochemists, Vincent Sarich and Allan Wilson, set out to put dates on the branching points in Goodman’s phylogenetic tree, applying the molecular clock theory developed by Zuckerkandl and Pauling. The prevailing wisdom among palaeoanthropologists, based on fossil evidence, was that the divergence between apes and the human line had occurred between 30 and 15 million years ago. The date that Sarich and Wilson came up with in 1967 was far more recent: 5 million years ago.
A running feud broke out between palaeoanthropologists and the molecular school. Outraged that molecular scientists should impinge on their own territory, palaeoanthropologists challenged the reliability of the molecular clock theory. The fossil record, they insisted, was a far more accurate measure. Addressing a meeting at the New York Academy of Sciences in 1968, John Buettner-Janusch of Duke University poured scorn on the molecular approach. ‘I object to careless and thoughtless statements about evolutionary processes in some of the conclusions drawn from the immunological data mentioned’, he said. ‘Unfortunately there is a growing tendency, which I would like to suppress if possible, to view the molecular approach to primate evolutionary studies as a kind of instant phylogeny. No hard work, no tough intellectual arguments. No fuss, no muss, no dishpan hands.