A new look at human ancestry

Deciphering human evolution from a few scraps of fossil bone has been likened to deducing the plot of Tolstoy's ''War and Peace'' from 13 randomly selected pages. Now an important new ''paragraph,'' if not an entire ''page,'' has been added.

It comes in the form of an apelike fossil from Pakistan. Dissenters from the traditional evolutionary scheme are likely to seize on it as further evidence that human beings and apes are so closely related that they shared a common ancestor a relatively short time ago.

In the traditional view, the evolution of apes and human beings diverged some 20 million years ago. On the path to humans, an apelike ancestor named Ramapithecus existed from about 14 million to 8 or so million years ago. This led to an upright-walking creature, Australopithecus, and eventually to humans.

During the past two decades, however, increasingly precise studies of biological molecules - both in living species and recovered from fossil bones - suggest a different story. These findings indicate that, because of so little biological difference between African apes - chimpanzee and gorilla - and humans , the human-African ape split occurred only about 6 million years ago. They further indicate that this African group shared a common ancestor with orangutans 10 million years ago and that all four shared common ancestry with gibbons 12 million years ago. All of these dates are uncertain by about 3 million years.

This evolutionary scheme suggested by molecular biology shatters the traditional view and has yet to be accepted generally by paleoanthropologists. In particular, it suggests that Ramapithecus cannot be a direct human ancestor. This is where the new fossil comes in.

It is a partial skull of an adult animal called Sivapithecus, with large parts of the face and palate, including all the teeth, preserved. Many experts now consider Sivapithecus and Ramapithecus to be the same thing. The skull was uncovered by a joint project directed by David Pilbeam, formerly of Yale and now at Harvard University, and S.M.I. Shah of Pakistan.

As Pilbeam describes the skull in Nature, it has many orangutan-like features. Cautiously, he says he prefers to await more fossil evidence ''before constructing evolutionary stories.'' Peter Andrews of the British Museum, London , is bolder in commenting on the find in the same issue of Nature. He says it helps clinch the conclusion that Ramapithecus ''can no longer be considered as part of the human lineage but as part of the orangutan lineage.'' He suggests Ramapithecines and orangutans are all part of a group that split from the path that led to the human-African ape group.

What appears to be an emerging affinity between Ramapithecus and the orangutan thus strengthens the case for considering humans and African apes a closely related group which only recently, geologically speaking, had a common ancestor. Thus there would seem to be no ''missing link'' between these apes and people.

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