On display in the lofty halls of the Transvaal Museum in Pretoria are some of the most important fossil specimens of our ancestors to be seen anywhere in the world. Yet visitors viewing the fossils, which are displayed alongside colourful models of apeman families tramping the grasslands of Africa, will find no mention of the word ‘evolution’. Instead, there is a verse from Genesis followed by references to a ‘zoological view’ of the ‘wonderful age-old process’ of creation, along with a variety of proposed trees for the descent of humans.
In South Africa, evolutionary theory is hugely controversial. The fundamentalist views of the Dutch Reformed Church held sway for more than 300 years, and today Darwin is still not taught in state schools. Nor is the situation likely to change in a hurry. Traditional African cultures have their own strong philosophies of life, and the new government has more pressing priorities. This blind spot over evolution is especially remarkable because South Africa is one of the world’s richest sources of hominid fossils.
For the past 70 years, researchers in South Africa have been at the forefront of palaeoanthropology – the study of human evolution. Yet they have had formidable barriers to combat, besides religion. The academic boycott during the apartheid years made it difficult to publish papers, attend international conferences or attract funding, and popular media outside South Africa took little notice of what was happening in science in the pariah state. Meanwhile, the charismatic Leakey family were making dramatic finds – including the first specimens of the earliest human, Homo habilis – in the magnificent setting of East Africa’s Great Rift Valley. This captured the imagination and rich support of National Geographic, and the Leakeys’ interpretation of human origins came to dominate debate in a subject that is fraught with professional rivalry.
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‘It was fashionable to turn one’s sights on East Africa, to the virtual exclusion of what was happening in South Africa,’ says Phillip Tobias, recently retired professor of anatomy and human biology at Johannesburg’s University of the Witwatersrand and now director of the Palaeoanthropology Research Unit at the university. ‘It’s only now that the academic boycott has ceased that we are being admitted back onto the planet again.’ With this readmission has come, at last, a recognition of the part South Africa has played in the long task of piecing together the jigsaw of our prehistory. Today, a mass of new discoveries, from bones to cultural artefacts, are contributing to novel interpretations of our past.
Even in the first half of the century, reports from South Africa were receiving a frosty reception from palaeontologists abroad. In 1924 the Australian-born anatomist Raymond Dart, then working at the University of Witwatersrand, found the fossilised skull of a child among the blasted rubble of a lime quarry at Taung (‘the place of the lion’) on the northeastern edge of the Kalahari. When he claimed it was the ‘missing link’ – something between ape and man, and a direct ancestor to ourselves – he was written off as a heretic. The prevailing view was that the first step in the evolutionary divergence of humans from apes was the development of a large brain. The theory was underpinned by the object known as Piltdown Man, supposedly a skull of one of our earliest ancestors but only later exposed as a hoax that had been concocted from a modern cranium and an ape’s jaws and teeth. The features of the Taung child were the reverse: it had a small brain, and jaws and teeth that were more human-like.
Dart’s discovery – the most significant for palaeoanthropology this century, according to some – challenged another orthodoxy: that the cradle of mankind was Asia, not Africa. This view had prevailed for 35 years, since Dutch anatomist Eugene Dubois found fossils in Java of an ancient hominid now known as Homo erectus, thought then to be about half a million years old. (In those days, dating was a matter of educated guesswork. We now know Java Man was dated at around 1.8 million years old.) The anthropological establishment dismissed Dart’s claim that the Taung child – which had been named Australopithecus africanus – had anything to do with the origin of humans.
Pivotal pelvis
After this rejection, Dart virtually gave up research on fossils. But in the 1930s Robert Broom, who had helped Dart analyse the Taung child skull, started to look for an adult A. africanus. Broom believed that an adult skull would vindicate Dart by showing more clearly the features that distinguish humans from apes – in this case, the teeth and the back of the skull – but which only develop with maturity.
Broom was working at the Transvaal Museum, and had to concentrate his search at fossil sites accessible from Pretoria. In 1936, he succeeded in finding such a specimen at Sterkfontein, a vast warren of limestone caves beneath the bleak, grassy hills of the Transvaal highveld near Johannesburg. At the same site he later found a pelvis of Australopithecus. This find offered clear evidence that Australopithecus had walked upright like modern humans (and unlike apes), adding grist to Dart’s mill.
But Sterkfontein – and Broom – are probably best known for the discovery in 1947 of another apeman, or rather apewoman. Broom believed it to be an adult A. africanus, but it was his habit to give different names to specimens from different places, so his find was attributed to a new genus, Plesianthropus. His paper describes the fossil, estimated then to be about a million years old, as that of an elderly female, and she was promptly nicknamed ‘Mrs Ples’ by the press. Being such a beautiful specimen, Mrs Ples caused a bit of stir, before the establishment dismissed her along with the Taung child as ‘just another ape’.
It was not until the mid-1950s, when the Piltdown hoax was exposed and more fossil evidence was starting to accumulate, that scientists began to look more closely at the claims of Dart and Broom. There were still doubts, however, and soon the South African work was being overshadowed by the numerous early hominid specimens unearthed by the Leakeys in the Rift Valley.
The turning point came in 1976, when Sterkfontein provided the first specimens of the genus Homo to be found outside East Africa. By then, Alun Hughes was in charge of the dig and he found fossils that were unmistakably H. habilis. These fossils could not be ignored or dismissed by the establishment in customary knee-jerk fashion, and they finally persuaded the sceptics – including the Leakeys – that South Africa’s fossil apemen, the australopithecines, were indeed part of the mainstream of human evolution.
After H. habilis was discovered at Olduvai Gorge in Tanzania in 1961, the Leakeys believed its immediate ancestor, too, would be found in East Africa, says Ron Clarke who took over responsibility for the Sterkfontein dig from Hughes in 1991. ‘But H. habilis is very similar to A. africanus,’ he points out, ‘and it’s clear now that H. habilis evolved directly from A. africanus.’
Fossils galore
Sterkfontein has yielded more than 500 specimens of early hominids, making it one of the richest fossil sites in the world. And with South Africa now recognised as a primary site of human evolution, its scientists have been able to concentrate on filling in the finer picture of our ancestors. In 1991, for example, archaeologist Kathy Kuman came across a rich deposit of stone tools in the caves, which she was later able to identify as belonging to H. habilis. This was the first sign in South Africa of the Oldowan stone tool culture, named after the Olduvai Gorge, where the tools were first found in the 1930s.
So sophisticated is the Oldowan culture that some people conjecture that it could only have been passed on from one generation to the next through spoken language. In 1980 Tobias went out on a limb, claiming he had found the physical evidence of language ability in H. habilis fossils. Brain casts, he said, show a marked fullness in the regions that control speech in modern humans, indicating that these crucial lobes were present in the earliest member of the genus Homo. No such speech centres are to be found in apes either ancient or modern, and before Tobias’s claims – which remain controversial – some had doubted whether even the Neanderthals of 40 000 years ago could speak properly.
In the same deposit as the Oldowan tools, Clarke has found what he believes to be Sterkfontein’s first fossil specimens of Paranthropus robustus (also known as Australopithecus robustus), a heavy-featured, beetle-browed apeman. The species coexisted in southern Africa with the earliest members of Homo some 1 to 2 million years ago, but its lifestyle and ultimate fate remain tantalising mysteries. (A sturdier cousin of P. robustus, known as Paranthropus boisei, lived around the same time in East Africa.)
Clarke also has the skull of a creature he put together from fragments found at different times in another deposit at Sterkfontein. From its date of around 2.5 to 3 million years ago and its colossal teeth, he believes he may have a completely new species that was an ancestor to P. robustus. But he has ‘held off naming him till I get a little more data’.
No name
Also awaiting identification is a partial skeleton of a hominid, including a large number of vertebrae, a collar bone and shoulder blade, arm bones, a sacrum and pelvis. ‘Such finds, before people started burying their dead about 100 000 years ago, are extremely rare,’ says Tobias. ‘In Africa only about six partial skeletons between the ages of 1 and 3.5 million years have been found. Maybe the carnivore that was eating this particular carcass was interrupted and didn’t tear it to pieces as it would normally do. The torso fossilised in position.’
Just across the valley from Sterkfontein is Swartkrans, another of the world’s classic sites. Swartkrans is also the source of fossils of H. habilis, along with more P. robustus remains than all the other sites put together and the first South African specimens of H. erectus (sometimes known as H. ergaster to distinguish it from later forms of H. erectus), all three species having coexisted at some point. First worked briefly by Broom in 1948, Swartkrans has been under the direction of Bob Brain since 1965 and its fossils are gradually building up to give a fascinating and unexpected picture of Paranthropus. Much of this important work, however, has gone unreported beyond the specialist scientific press.
In the 1980s, Brain’s team at Swartkrans found hand and foot bones in a deposit at Swartkrans dated at around 1.8 million years ago and attributed to Paranthropus. These fragile parts of the skeleton rarely survive intact and, remarkably, show that the apeman had fingers as nimble as our own, eminently capable of making and using tools. Furthermore, ‘he was as capable of walking on two legs as other contemporary hominids and probably spent most of his time on the ground, not in trees’, according to Randall Susman of the State University of New York at Stony Brook, who analysed the bones.
Wear and tear
Brain believes Paranthropus probably had bone tools which he used to dig lily bulbs from crevices in the rock. He tested this hypothesis by asking his son Conrad, then a small boy, to dig bulbs from the earth round Swartkrans with shafts of bone similar to the fossils found in the caves. The wear marks on the contemporary tools proved to be identical to those found on the fossils. These discoveries dealt a blow to the view then prevailing that it was the making and use of tools that gave our ancestors H. habilis and H. erectus the edge over Paranthropus – who had shared the same habitat and resources for millennia – and led to his extinction around a million years ago.
A new twist to the mystery of early Homo’s relationship with Paranthropus emerged in 1986, when Brain came across burnt bone at Swartkrans – layer upon layer of it – in a deposit 6 metres thick and dated somewhere between 1 and 1.5 million years old. The fragments, which looked as though they had been in a campfire, came mainly from large antelopes, warthogs, zebras and baboons. This is the earliest evidence of the controlled use of fire, predating by perhaps a million years the records of fire associated with Peking Man (H. erectus) 400 000 years ago in Zhoukoudian, China.
The mystery lies in the fact that the only hominid remains found in the same layers as the burnt bones are of Paranthropus. Could the apeman therefore have been the first fire user? Brain finds this explanation unlikely, and sees H. erectus as the more plausible user of the fire. The reason no trace of H. erectus is found in the same deposit as the burnt bone, he says, is that camp fires afforded them protection from predators. For once they were not being eaten round Swartkrans, so no bones were left to fossilise.
Brain believes it was probably fire that gave people the edge over apemen, and indeed all other living creatures. ‘The earlier deposits at Swartkrans, as elsewhere in South Africa, are carnivore-dominated,’ he points out. ‘The primates were a small, insignificant part of the whole setup until they started to develop their technology. Then, when they could set fire to hillsides, burn their prey out of thickets and that sort of thing, the balance of power tipped.’
Brain’s preoccupation with the context in which fossil hominids are found, and the clues this gives to the environment they inhabited, has inspired the new generation of palaeoanthropologists. ‘Bob Brain revolutionised the way we dig a cave,’ says Lee Berger, who is overseeing the digging at Gladysvale, about 50 kilometres west of Johannesburg in the same limestone ridge as Sterkfontein and Swartkrans. Gladysvale overlooks a beautiful stretch of hills studded with thorn trees and shaggy aloes on a private game reserve, and in 1992 it became South Africa’s first new hominid site since 1948.
‘A large part of our job,’ says Berger, ‘is understanding the world these hominids lived in.’ This is palaeoecology – the search for clues to climate, vegetation and other creatures that lived at a particular time – and it is the approach Berger is taking in his excavations.’ We spend most of our time looking at the bones of one order of animal, primates,’ says Berger. ‘But these things didn’t exist in a vacuum. It’s vital to recognise that all the work in interpreting form and function of a bone is wasted if the environment wasn’t capable of supporting that behaviour.
On almost their first visit, Berger’s team picked up a tooth of A. africanus in perfect condition. Gladysvale has since yielded specimens of early Homo that have yet to be described and published, but one of its most valuable contributions may be in dating South African fossils. Unlike the volcanic lake beds and river sediments of East Africa, the limestone caves in which the South African fossils are found cannot be accurately dated using traditional methods that rely on radioactive decay. Instead, the age of bones has to be gauged by association with the other flora and fauna in the deposit. The picture is complicated by the fact that deposits are not laid down in neat layers, and cave contents constantly rearrange themselves as a result of water erosion. Moreover, the caves were originally opened up by lime quarriers, so many of their fossil riches were tossed out with the rubble. At Gladysvale, by contrast, parts of the deposits – which span a time from perhaps 3 million years ago to the present – are uniquely unjumbled and so offer a rare opportunity for accurate dating.
Switching dates
Berger is busy soliciting funds and assembling a specialist team. It will probably try palaeomagnetic dating first. This involves drilling through the deposits, taking a core, and looking at the magnetic orientation of particles at different levels to try to detect the ‘reversals’ – the points in time when the Earth’s magnetic poles switched so that north became south and vice versa. Because the dates of these reversals are known, they could give a more precise chronological framework to the analysis of South Africa’s fossil record.
In a field where vivid imagination has until now been a prime qualification, modern technology holds out the prospect of certainties where once there was only guesswork, says Tobias. For example, by using CT scanners to look at the internal morphology of fossil skulls, palaeoanthropologists are getting the kind of fine detail that could resolve some of the battles about the relationships between species and help overcome historic rivalries between East and South Africa.
Francis Thackeray of the Transvaal Museum is collaborating with the East Africans on a project aimed at scanning all the unworn hominid molars and premolars collected from both regions to build a database of up to 40 measurements per tooth that will help to define species. Already CT scanning has been used to study the stage of development of unerupted teeth in the jaws of the Taung child, to establish its age when it died. It is now believed to have been about three years old; Dart’s estimate was six.
On the other hand, modern technology could lead to new arguments if it comes up with evidence that challenges received ideas. Now out of the shadows, South African fossils and scientists are bound to play a dynamic and visible part in trying to solve this and other great mysteries.
Sue Armstrong is a science writer based in South Africa.
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South Africa’s hominid fossil sites
Taung The first specimen of Australopithecus africanus, a child, found 1924. Excavation resumed in 1988; no new hominid fossils found so far, but new light shed on dating Taung child.
Sterkfontein Excavated on and off since 1930s. Most famous fossil ‘Mrs Ples’, found 1947. Extremely rich site for hominids, including the genus Homo. First Oldowan stone tools outside East Africa found here in 1991.
Swartkrans Excavated from 1948 to 1952 and from 1965 to present. World’s richest site for Paranthropus robustus. Earliest evidence of controlled use of fire discovered 1987.
Makapansgat Excavated from 1948 to 60. New dig commenced 1993. Analysis of more than 7000 fossil bones, predominantly antelope, found in the same deposits as A. africanus, led Raymond Dart to suggest in 1957 that our ancestors were weapon-wielding hunters who dominated the landscape. The hypothesis has been strongly challenged and is no longer widely accepted.
Kromdraai First specimens of P. robustus found in 1938. Many specimens of Australopithecus found in sporadic excavations since.
Gladysvale First visited in 1936 by Robert Broom. Excavated briefly in 1950s. Excavations resumed 1992, when first hominid fossils found.
Driemeulen First excavated in 1992, and appears to be a rich site for P. robustus.
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Turning over evolution
The extra scope offered by computers for analysing data is allowing palaeontologists to challenge some widely accepted hypotheses. One such is the ‘turnover-pulse hypothesis’ of evolution proposed by Elizabeth Vrba of Yale University, which has come under attack from Jeff McKee, leader of the Hominid Palaeoecology Research Unit at Witwatersrand University. Vrba’s hypothesis holds that the first appearances and extinctions of species seen in the fossil record coincide with dramatic changes of climate at certain points, and that these climatic changes are the cause of evolution (‘Taking the pulse of evolution’, Â鶹´«Ã½, 24 July 1993). According to this hypothesis, a climatic event around 2.6 million years ago led to the emergence of the genus Homo and our evolutionary divergence from the australopithecines.
However, evidence of A. africanus, dating from around the same period, has come from both the semidesert site at Taung and the richly vegetated site at Makapansgat, 250 kilometres north of Johannesburg. This has led McKee to question whether climatic change could have caused human evolution, given that our ancestors could live in such diverse environments. First and last appearances of mammals in the South African fossil record certainly suggest that there were ‘pulses’, he says. And they correlate with supposed climatic events. But couldn’t this just be coincidence?
McKee tested the idea by running computer simulations of the evolution of various species of mammals proceeding steadily and gradually – that is, according to a constant turnover model – and took a random sample of the results of these simulations to mimic the incomplete fossil record that is observed in reality. He then did the same for a turnover-pulse model of the evolution of the same species. To his astonishment, the constant turnover model indicated emergence and extinction of species that were closer to the observed data from South Africa’s fossil sites than those produced by the turnover-pulse model. ‘I just sat there are shivered,’ he says. ‘I couldn’t believe how close it was to reality.’
To test his belief that evolution is a constant rather than a punctuated process, McKee now intends to run simulations based on the East African fossil record and see which of the two models is closest to reality. ‘Darwin was adamant that climatic change did not cause evolution,’ says McKee. ‘What I’m saying now is that evolution will occur whether there’s climatic change or not. But what did cause evolution, I have no idea.’