New fossil find changes thinking on man’s roots

Press, 13 April 1982, Page 20

New fossil find changes thinking on man’s roots

From the “Economist.” London _

A remarkable fossil has been scooped out of the Siwalik Hills in Pakistan: No fossil so complete exists for a 14M-year period of man's evolution extending from 18M years ago to after 4M years ago. But there is bad news. too. This fossil—and, presumably, less complete ones like it—- • turns out to be similar to modern orang-utans. It is not an ancestor of man and leaves a 14M-year gap, in knowledge of man’s lineage. The fossil's discovery has been reported- in Nature magazine by Dr David Pilbeam, a Harvard scientist and one of the leading experts on fossils of this period. He has been scouring the Siwalik Hills with a large team of helpers since the ’ early 19705. The fossil is eight million years old and probably is from an animal which li'vedmostly in trees. It belongs to a species named Sivapithecus indicus.

In the past, desire for fame has tempted fossil hunters to attribute too many of their finds to a previously undiscovered species.. Consequently, a bewildering number of species names describes fossils that are actually very similar. Sivapithecus differs only in size from species of Ramapithecus. These C"ramapithecine” apes lived in a wide area of Asia and Europe, and a few specimens have also been found in Africa.

Previously it was accepted wisdom that ramapithecines were the ancestors of man and his close cousins, gorillas and chimpanzees. Many

graphic accounts have been written .of how the decline of tropical rain forests tempted ramapithecines down from the trees to spend part of their time on the ground. Many drawings have been published of bent-backed ramapithecines taking the first steps towards walking upright.

the trouble is that, till recently, all the known remains of ramapithecines would fit in a shoe box. Furthermore virtually all these fossils were either teeth, or jaw fragments. Experts were making too much of such slender evidence as the thickness of tooth enamel.

Dr Peter Andrews of London's natural history museum, was an early sceptic.

The key experts on these fossils are now mostly convinced that ramapithecines are a side issue, as far as man’s family tree is, concerned. For most Dr Pilbeam’s Siwalik discovery is the clinching evidence. Even Dr Elwyn Simons, once a staunch apostle for Ramapithecus, is now not so sure of its closeness to man on, the family tree. The trouble is there are no other strong candidates to replace the role of ramapithecines in man’s ancestry. Gigantopithecus, another member of the ramapithecine group, is an unlikely candidate. Known mostly from China, where fossil tee’th used to be prized as dragon’s teeth, Gigantopithecus w*as possibly much larger than a gorilla and died out only 0.5 million years ago.

What does now seem as certain as anything in this field is that Dr Pilbeam’s fossil is too like an orangutan to be a direct ancestor of man. Man and the African apes split from a common stock much later than orangs split from the African apes. One possibility is that the ramapithecines.' which seem so similar to one another on current fossil evidence, were actually a much more mixed bunch of species. It could be that the similarities, based on jaws and teeth, are misleading. When other specimens as complete as Dr Pilbeam’s fossil are found, they may prove to be quite different from his. Indeed. Dr Simons claims that fossils from China as yet unreported, show some features that are less ■ orang-like than the Siwalik fossil.

Another possibility is that man and African apes sprang from stock that is still undiscovered. Apes of all species seem to have been comparatively rare between 18 million and four million years ago. They were more plentiful both before and after this period.

This scarcity implies that scientists may need to do a lot of searching before finding a direct ancestor of man from this period.

Dr Pilbeam likens the search to the drilling programme by which scientists are exploring the ocean floor. He says that all his years of work in the Siwalik Hills are equivalent to lowering one borehole into the floor of the Altantic. Many more boreholes will be

needed to find man’s last common ancestor with the apes.

Dr Pilbeam has just sent a team to sink such a borehole near Lake Barringo in Kenya. The rocks there are dated 14M-4M years old. Mr Richard Leakey also hopes to explore a new site in Kenya with rocks older than the fossils previously found in Africa. There are other sites of similar antiquity in Ethiopia and west Africa. From 4M years ago, man’s emergence is now comparatively well documented in African fossils. By that time, man was already walking upright. Though his brain was no larger than an ape’s he had split off from his previously common descent with African apes. The big advance in research during the 1970 s was to increase many-fold the number of fossils from 4M years ago until the recent past. Though there are still questions to be answered about this period, the biggest task now is to extend the record back before 4M years ago, over a period of several million years when the fossil evidence of proto-men or apes in Africa consists of little more than the occasional tooth.

Yet this was a period of dramatic changes in Africa, in terms of climate, geology and ecology. Such, period's provide abundant opportunities for species of animals to begin new evolutionary initiatives. Eventually a common ancestor of both man and African apes should be discovered. But to expect to find a fossil of the first man may be asking too much.