Up From The Apes

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All told, the scientists excavated the bones and teeth of 17 individuals. Given their age, no one was surprised that they showed a mix of chimpanzee-like and human traits that as a whole are more primitive than those of A. afarensis: smaller molars, larger canines and thinner tooth enamel, suggesting a diet rich in easy-to-chew fruits and vegetables. The new species, says paleontologist Tim White of the University of California at Berkeley, a co-leader of the expedition, "is way closer to an ape than to an australopithecine and is significantly different from any other hominid."

Because the fossils were too distinctive to be included in Lucy's extended Australopithecus family, the researchers called the new species Ardipithecus ramidus (ardi means ground or floor in the local Afar language, and ramid means root). White and his colleagues have since found other ramidus fossils at their site but are giving out precious few details until they complete their methodical analysis of the bones. Says ramidus co-discoverer Berhane Asfaw of the Rift Valley Research Service in Addis Ababa: "It will be worth the wait."

One prize specimen, they acknowledge, is a partial skeleton found by Berkeley graduate student Yohannes Haile-Selassie (no relation to the Emperor). Alas, the back of the skull is badly crushed. A hippo or elephant probably trampled it soon after the creature died. "It looks like roadkill," quips White. Given the small skulls of A. afarensis and other later australopithecines, however, this specimen undoubtedly had a pint-size brain. At this point in evolution, says White, "we're in the minor leagues of brain development."

But the skeleton does include many bones that will help White's team answer the much more important question of how Ardipithecus got around. Paleoanthropologists believe that bipedalism was the first significant modification separating our ancestors from the great apes. By studying the bones and fossil footprints of A. afarensis (Lucy and her line) as well as those of half a dozen other australopithecine species, scientists already knew that our ancestors walked upright long before they acquired other human traits--and that bipedalism gave them a huge edge.

According to conventional wisdom, this evolutionary breakthrough came at a time when climate change was transforming eastern and southern Africa from dense forest into open grassland. Standing upright in such an environment could have offered our ancestors many advantages. It could have let them scan the horizon for predators, exposed less body surface to the scorching equatorial sun (and, conversely, more to the cooling wind) or freed their hands for carrying food.

But these ideas may be in trouble. Fossilized seeds, petrified wood and animal bones found by White and his colleagues at the digging site, near the village of Aramis, indicate that it was quite densely wooded when A. ramidus lived there. If the hominid turns out to have been bipedal, as preliminary studies indicate, this could wash away existing theories--though the scientists can't say for sure until other hominid fossil sites of comparable age are found.