Artificially Reconstructed "Ardi" Overturns Prevailing Evolutionary Hypotheses of Human Evolution - Evolution News & Views

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Artificially Reconstructed "Ardi" Overturns Prevailing Evolutionary Hypotheses of Human Evolution

The missing link presently being touted in the media, Ardipithecus ramidus, has had more reconstructive surgery than Michael Jackson. Assuming that their "extensive digital reconstruction" of its "badly crushed and distorted bones" is accurate, what does A. ramidus (or "Ardi" as the fawning media is affectionately calling it) really show us that we didn't already know? We already knew of upright walking / tree-climbing, small-brained hominids--that's what Lucy, an australopithecine, was. We already knew that there were australopithecine fossils dating back to before 4 million years, and this fossil is only a little bit older. So what does this fossil teach us? Assuming all the reconstructions of Ardi's crushed bones are objective and accurate, this fossil teaches us at least one very important thing: prevailing evolutionary explanations about how upright walking supposedly evolved in humans, confidently taught in countless college-level anthropology classes, were basically wrong.

In particular, A. ramidus casts doubt on the long-repeated hypothesis that humans evolved upright walking on the African Savannah where taller creatures had an advantage to see over tall grass by walking upright. A. ramidus walked upright in a "grassy woodland with patches of denser forest." Time magazine's article on A. ramidus explains the implications:

This tableau demolishes one aspect of what had been conventional evolutionary wisdom. Paleoanthropologists once thought that what got our ancestors walking on two legs in the first place was a change in climate that transformed African forest into savanna. In such an environment, goes the reasoning, upright-standing primates would have had the advantage over knuckle walkers because they could see over tall grasses to find food and avoid predators. The fact that Lucy's species sometimes lived in a more wooded environment began to undermine that theory. The fact that Ardi walked upright in a similar environment many hundreds of thousands of years earlier makes it clear that there must have been another reason.

(Michael D. Lemonick and Andrea Dorfman, "Excavating Ardi: A New Piece for the Puzzle of Human Evolution," Time Magazine (October 1, 2009).)

In fact, this is an old argument. It's rarely discussed, but there are a number of upright-walking, forest-dwelling ape-like species known from prior to 10 million years ago that are thought to be far removed from human ancestors. This implies that bipedalism in a hominoid does not necessarily qualify an individual as a human ancestor, and it also casts doubt on classical explanations for the evolution of bipedalism.

There is one other option: A. ramidus wasn't bipedal. In fact, one Science article is reporting some serious scientific skepticism about A. ramidus being bipedal:

However, several researchers aren't so sure about these inferences. Some are skeptical that the crushed pelvis really shows the anatomical details needed to demonstrate bipedality. The pelvis is "suggestive" of bipedality but not conclusive, says paleoanthropologist Carol Ward of the University of Missouri, Columbia. Also, Ar. ramidus "does not appear to have had its knee placed over the ankle, which means that when walking bipedally, it would have had to shift its weight to the side," she says. Paleoanthropologist William Jungers of Stony Brook University in New York state is also not sure that the skeleton was bipedal. "Believe me, it's a unique form of bipedalism," he says. "The postcranium alone would not unequivocally signal hominin status, in my opinion." Paleoanthropologist Bernard Wood of George Washington University in Washington, D.C., agrees. Looking at the skeleton as a whole, he says, "I think the head is consistent with it being a hominin, ... but the rest of the body is much more questionable."

(Ann Gibbons, "A New Kind of Ancestor: Ardipithecus Unveiled," Science, Vol. 326:36-40 (Oct. 2, 2009).)

Likewise the Chronicle of Higher Education is reporting:
Mr. Johanson, founding director of the university's Institute of Human Origins ... said, he expected the team's initial interpretations "will undoubtedly generate widespread debate," perhaps even including the question of whether Ardi is actually a human ancestor. Mr. Johanson said he was not among those who would raise that question. But, he said, "there must have been very rapid evolutionary change" for the human form to transform so quickly from Ardi to Lucy.
Of course, virtually none of this serious scientific skepticism about bipedality or ancestral status in A. ramidus is being reported in the mainstream popular media, where the species is essentially being universally reported as an upright-walking hominid ancestor of modern humans. Ardi thus leaves us with 2 options: either she wasn't an ancient upright walking hominid and isn't anything close to a human ancestor, or our previous--and confidently touted--theories about how bipedality evolved in humans were wrong. Take your pick.

So what do we have with "Ardi"? We have an extremely crushed "Irish stew" fossil that has undergone extensive reconstruction in order to become part of a PR campaign to make bold claims of ancestral status to the human line, even though at base its qualities are very similar to previously known fossils, and there's a lot of skepticism about the claims being made. In other words, we have the typical media circus that we find every time a new "missing link" is found.