Ardipithecus ramidus  (Source: Science/AAAS)

There is debate over what exactly the habitat of Ardi, a "missing link" ancestor of man, was and whether Ardi was truly a hominid.  (Source: Science/AAAS)
Scientists welcome healthy debate; creationists cheer opportunity to attack discovery

The publication of the groundbreaking Ardipithecus ramidus, or "Ardi", skeleton in 2009 was one of the most important scientific discoveries of its closing decade.  The skeleton offered new insight into the evolutionary path of man.  It also provoked a great deal of debate, both scientific and theological as such a find might be expected to.

Now two commentaries have been published debating the accuracy of two of the key conclusions of the original study [published here] -- Ardi's place on the evolutionary tree and the habitat that it lived in.

The first study is the less controversial, in that it merely argues that rather than a forest habitat, as the original study suggests, that Ardi instead lived in savanna.  Thure E. Cerling, a geochemist at the University of Utah, spearheaded this work which is published here as a comment in the journal 

In the comment, Cerling writes, "We find the environmental context of Ar. ramidus at Aramis to be represented by what is commonly referred to as tree- or bush-savanna, with 25 percent or less woody canopy cover."

Key to Cerling's claim is the fact that Ardi was found with less woody plant matter than is typically expected from a dense forest.  And historical theory favors Cerling's claims, as scientists have long argued that hominids (including man) evolved in a savanna setting, likely in Africa.

White's team has published a response in 
Science arguing against this perspective and defending its original assertions that Ardi lived in a woody setting.  White writes that Cerling's comment failed to account "the totality of the fossil, geological and geochemical evidence."  Key to White's argument are other mammal fossils found alongside Ardi that were creatures which typically lived in denser forest.

Esteban E. Sarmiento of the Human Evolution Foundation in East Brunswick, N.J., by contrast, offered up a more controversial challenge.  He claims that Ardi was not a hominid -- a creature in the evolutionary path that gave rise to modern chimpanzees and man.  He claims Ardi, which lived 4.4 million years ago, "predates the human/African ape divergence."

Sarmiento's criticism is published here.  The claims were promptly refuted by White's team, which argues that they fail "to recognize as significant the multiple and independent features of the Ardipithecus cranium, dentition and skeleton."  White's rebuttal also comments that they use outdated biomolecular evidence and that current evidence pushes the data of hominid/ape divergence from 3 to 5 million years ago back to 6 million years ago.

Such debate is absolutely business as usual for such a high profile work.  And if there's one common thread between the critics and original authors, it's that they both agree that the biochemical and fossil evidence clearly points to evolution giving rise to humans.  The debate is merely on the path that was taken, where the fossil fall on that path, and what the environment those historical creatures lived in.

Creationists have quickly latched on to this healthy scientific debate as signs of "flaws" in evolutionary theory.  As one critic commenting on a 
CBS story on Ardi comments, "[Well], just more evidence for the growing stack of evidence that the theory of evolution is bogus. But of course the knowledgeable knew that long ago."

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