Born in Africa

WHAT BECAME known as ‘The Battle of the Bones’ began in January 1979 when an article by Johanson and White explaining their new interpretation of the origins of humankind was published as the main feature in the American journal Science, prompting widespread media interest. The press reported that ‘a previously unknown human ancestor’ combining a small-brained apelike head with a fully erect body had been discovered in Africa. In a front-page article, the New York Times pointed out that the new species—Australopithecus afarensis—presented a major challenge to conventional theories about human evolution.

Among the anthropological community, opinion about the merits of the Johanson-White hypothesis was divided. Attacks came from several different quarters. Richard Leakey rejected the notion that Australopithecus afarensis was the common ancestor of all later australopithecines and Homo; the common ancestor, he said, had not yet been found. He was ready to accept that Lucy was a new species of australopithecine; but he maintained that among the other Hadar fossils were examples of two different populations: Homo and Australopithecus. And he held fast to his view that the Homo lineage had much deeper origins than the 2-million-year threshold proposed by Johanson-White.

Mary Leakey’s response was far sharper. Furious at the way Johanson and White had purloined the Laetoli fossils for their own use, she dismissed their work at a Washington press conference in March 1979 as ‘not very scientific’. She believed that their real purpose was not so much to establish a link between the Hadar and Laetoli fossils as to secure for afarensis the older, proven date of the Laetoli fossils. The obvious choice for a type specimen for afarensis, she pointed out, was not LH-4 from Laetoli but Lucy. ‘It is regrettable’, she told Roger Lewin, ‘that the type specimen selected should be a worn mandible from Laetoli, when much better-preserved specimens are available from Afar itself’.

Other scientists lined up to support her. The American geologist Richard Hay described the use that Johanson-White had made of the Laetoli fossils as ‘a form of scientific theft’. The eminent zoologist Ernst Mayr, an expert on taxonomy, was scathing about the way they had taken the type specimen from Tanzania but the name from Ethiopia. ‘If you select a geographical locality for the name, then you have no choice but to select the type specimen from the same locality’. The two sets of fossils were located 1,000 miles apart and separated by half a million years in time, leaving open the possibility that they were geographic variants induced by climatic and other environmental conditions. ‘Every species consists of numerous local populations differing to the degree of their isolation’. The proper decision therefore, said Mayr, would have been to name Lucy as the type specimen. ‘It was a horrible thing that Johanson did’, he told Virginia Morell, ‘... and made everyone’s hair stand on end’. He wanted the International Commission on Zoological Nomenclature to suppress Johanson’s type designation and designate instead a specimen from Afar.

Further doubt about the Johanson-White hypothesis was cast by Yves Coppens, the French co-leader of the Afar expedition who had previously agreed to be listed as a joint author in the naming paper published by Kirtlandia. Coppens published an article saying that, like Richard Leakey, he recognised at least two species among the Hadar fossils, not just one. As well as bones belonging to afarensis, he detected a primitive species of Homo present, too.

From South Africa, Phillip Tobias, Professor of Anatomy at the University of the Witwatersrand, weighed in with his own broadside. Tobias saw no reason Australopithecus africanus should be usurped by afarensis as the progenitor of all later hominids. The Laetoli and Hadar hominids, he declared, were indeed subspecies, but of africanus not afarensis. He suggested that the Hadar hominids should be named Australopithecus africanus aethiopicus and the Laetoli hominids Australopithecus africanus tanzaniensis. Addressing an international scientific meeting in London in March 1980, he called for the term afarensis to be scrapped: ‘Since the tying of the name “A. afarensis” to the Laetoli fossils is manifestly inappropriate and since it is considered that the case for “A. afarensis” has not been established, it is proposed formally that the name “A. afarensis” be suppressed’.

Despite all the hubbub, the Johanson-White hypothesis gradually gained favour, and Australopithecus afarensis duly became accepted by most of the scientific community as the oldest member in the pantheon of ancient ancestors yet discovered. The picture that emerged was of a hominid weighing from seventy-five to 125 pounds, between three and four feet tall, with a brain volume of between 400 and 500 cubic centimetres, only a little larger than the average brain size of a chimpanzee.

After studying the Hadar hominids, Owen Lovejoy, an expert on the biomechanics of locomotion at Kent State University in Ohio, concluded that afarensis hominids were well-adapted bipeds. ‘They look incredibly primitive above the neck and incredibly modern below. The knee looks very much like a modern human joint; the pelvis is fully adapted for upright walking; and the foot, although a curious mixture of ancient and modern, is adequately structured for bipedalism. Some of the bones in the feet are slightly curved, and look rather like the bones you’d expect to see in its ancestor who climbed trees. But I believe that the curvature in the afarensis foot bones is well suited for walking on soft, sandy terrain; it probably inherited the curved feet from its tree-climbing ancestors, but the shape has been made use of in a different way’.

The upright gait of afarensis led many palaeoanthropologists to conclude that Lucy and her kind, though descended from treedwelling ancestors, were terrestrial creatures that spent their whole time at ground level. But further studies by researchers at the State University of New York at Stony Brook presented a different picture. They agreed that while on the ground, Lucy had clearly functioned as a biped. But they noted that Lucy possessed relatively long arms, apelike shoulder joints, powerful wrists and curved toes, all suggesting that afarensis retained a tree-climbing capacity and still spent a good deal of time in the trees.

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. Just throw some proteins into the laboratory apparatus, shake them up, and bingo!—we have an answer to questions that have puzzled us for at least three generations’.

But further research by Sarich and Wilson, involving DNA molecules as well as proteins, confirmed the validity of their original approach. ‘One no longer has the option of considering a fossil specimen older than about eight million years a hominid, no matter what it looks like’, proclaimed Sarich in 1971.

For more than a decade, many palaeoanthropologists fought a rearguard action against the molecular school but steadily lost ground. By the early 1980s, a new family tree using molecular techniques had gained widespread acceptance. It showed the ancestor of gibbons splitting off first from the line leading to humans more than 20 million years ago; followed by the ancestors of orang-utans splitting off at 16 million years ago; by gorillas at about 10 million years ago; by chimpanzees at between 6 and 7 million years ago; and finally, by australopithecines splitting off from the line leading to early Homo at between 3 and 4 million years ago.

While the molecular revolution was gathering momentum, new schools of thought were emerging about the process of evolutionary change. Since the 1950s, the ruling doctrine to which most scientists subscribed was the evolutionary, or modern, synthesis, the theory that viewed evolution as the steady accumulation of small genetic changes over long periods of time under the guiding hand of natural selection. Its defining feature was gradualism. New species were the result of gradual change involving a whole population.

But in 1972, two American invertebrate palaeontologists, Niles Eldredge of the American Museum of Natural History and Harvard University’s Stephen Jay Gould, presented a counter-theory. From his studies of trilobites—fossil marine arthropods dwelling on the sea bottom—Eldredge had noticed a distinct lack of evolutionary change; for millions of years, one type of trilobite had remained unaltered until environmental change had enabled a new species to invade and replace it. Gould had observed the same kind of pattern from his studies of an ancient species of land snail. It appeared to both of them that evolutionary change occurred not so much as part of a gradual process but in relatively short sporadic episodes, with most change being concentrated in branching events in a geographically restricted subset of a population. Once evolved, new species, with their own peculiar adaptations, behaviours and genetic systems remained unchanged for long periods of time, often for several million years. In a paper published in 1972, they called this process ‘punctuated equilibrium’ and posed it as an alternative to the doctrine of ‘phyletic gradualism’.

They claimed that their theory provided a more convincing explanation of the gaps that seemed to occur in the fossil record than the one given hitherto by the ‘gradualist’ school. They pointed out that if evolution had occurred as a result of slow, gradual and continuous change over the generations, as the gradualists maintained, then the fossil record should show it. But the record appeared to contain gaps. In the past, these gaps had been attributed to the difficulty that researchers faced in finding enough fossils to fill in the record. But even though a plethora of fossils had since been discovered, the ‘gaps’ were still said to be there. The explanation, said Eldredge and Gould, was that evolution occurred in bursts of change followed by long periods of stasis, or non-change. What the fossil record showed, they argued, was ‘breaks’ in the pattern of evolution, not missing links; in some cases, changes may have occurred so rapidly that intermediate forms had not been preserved in the fossil record.

They also contested the gradualist assertion that human evolution had occurred as a straight line of continuous transformation of one species into the next. They argued instead that human evolution resembled a multibranched bush of diversity, with many species coming into existence and almost as many dying out.