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Is “Ardi” All Washed Up? (Updated)

In some ways, the career of a missing link mirrors the career of the celebutante. They break onto the scene with much fanfare and hype. Everyone is wowed–or at least, everyone pretends to be wowed so nobody can be accused of ruining the party. Besides, she’s useful for advancing lots of agendas. After a little while, people realize that the star doesn’t have all the talent everyone hoped for. Nobody wants to feign excitement anymore. Eventually, people are sickened of the original hype and become eager to see the celebutante fall. And then it’s the fallen celebutante that starts making headlines. Substitute the word “missing link” for “celebutante” and this is something like what we’re now seeing with “Ardi,” the once-purported “oldest human ancestor.”

Last fall “Ardi” came onto the missing link scene with a bang. The journal Science called her the “breakthrough of the year.” So did Time Magazine. We covered a few lone dissenters to the Ardi hype here on ENV.

But now Time Magazine is starting to go over apex of the hype curve. In an article titled, “ Ardi: The Human Ancestor Who Wasn’t?,” Time notes, “Two new articles being published by Science question some of the major conclusions of Ardi’s researchers, including whether this small, strange-looking creature is even a human ancestor at all.” Likewise, Nature reports, “Ardi may be more ape than human.” According to the Time article:

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.”

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.

Update: One important point from Sarmiento’s paper that Time failed to mention is the fact that the paper also challenges the all-important claim that Ardi walked upright:

Moreover, attempts to link Ar. ramidus to an exclusive human lineage by pointing to suspected facultative bipedal characters in the foot are not convincing. All of the Ar. ramidus bipedal characters cited also serve the mechanical requisites of quadrupedality, and in the case of Ar. ramidus foot-segment proportions, find their closest functional analog to those of gorillas, a terrestrial or semiterrestrial quadruped and not a facultative or habitual biped.

(Esteban E. Sarmiento, “Comment on the Paleobiology and Classification of Ardipithecus ramidus,” Science, Vol. 328:1105 (May 28, 2010).)

Another paper in Science challenges the claim that Ardi lived in a wooded environment.

While these are relatively muted attacks on Ardi, they nonetheless show that the hype is wearing off. As Time notes, “Sarmiento regards the hype around Ardi to have been overblown.”

Given that these fossils come from the realm of science and not the world of celebrity gossip, why is the hype necessary in the first place? Discover Magazine is now saying “The bones of our ancestors do not speak across time with ultimate clarity.” That’s an understatement–but given how everyone previously fawned over Ardi’s so-called “missing link” status, could it be that there is more than mere science driving the promotion of these supposed transitional forms?