A reconstructed frontal view of Ardi
Reuters / Corbis
Neither article challenges the veracity of the evidence published by the team of scientists, led by paleoanthropologist Tim White of the University of California, Berkeley, which painstakingly pieced Ardi together from more than 100 crushed fossil fragments. But they do dispute the conclusions White and his colleagues reached from that evidence.(See the top 10 scientific discoveries of 2009.)
In the first article, titled "Comment on the Paleobiology and Classification of Ardipithecus ramidus," Esteban Sarmiento, a primatologist at the Human Evolution Foundation, argues that many of the "characters" — the scientific term for physical traits — used by White to place Ardi on the human lineage are also shared by other primates. He argues that the evidence suggests Ardi belongs to a species that evolved before the moment when humans, apes and chimps diverged along different evolutionary paths. That is significant because one of the things that made Ardi interesting scientifically was that she had been identified by White as the earliest known descendant of the last common ancestor of humans and African apes — thus her physiology could offer clues to what makes humans different from their nearest relatives.
"[White] showed no evidence that Ardi is on the human lineage," Sarmiento says. "Those characters that he posited as relating exclusively to humans also exist in apes and ape fossils that we consider not to be in the human lineage."(See how Ardi was first discovered.)
The biggest mistake White made, according to the paper, was to use outdated characters and concepts to classify Ardi and to fail to identify anatomical clues that would rule her out as a human ancestor. As an example, Sarmiento says that on the base of Ardi's skull, the inside of the jaw joint surface is open as it is in orangutans and gibbons, and not fused to the rest of the skull as it is in humans and African apes — suggesting that Ardi diverged before this character developed in the common ancestor of humans and apes.
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