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The Overselling of Ardipithecus ramidus

By Casey Luskin

If you believe what you read in the newsmedia, another new alleged missing link has been found. That is, if you consider something discovered in the early 1990’s new. This fossil seems to have spent almost as much time under the microscope at Berkeley as it did in the ground in Ethiopia, when it was first buried about 4.4 million years ago.

Why did it take over 15 years for the reports on this fossil to finally be published, besides the fact that it allowed more time for planning the now-customary PR campaign? A 2002 article in Science explains exactly why: the bones were so brittle, “squished,” “chalky” and “erod[ed]” when cleaned such that many of the bone fragments had to be “reconstruct[ed]”—and that took a long time. Here’s the story from more than seven years ago: [I]n 1992, the Middle Awash Research Team, co-led by [Tim] White, made a discovery that ended Lucy’s reign. About 75 kilometers south of Lucy’s resting place, at Aramis in the Afar depression of Ethiopia, the team found fossils of a chimp-sized ape dated to about 4.4 million years ago. … The team named this species Ardipithecus ramidus, drawing on two words from the Afar language suggesting that it was humanity’s root species. But skeptics argue that the published fossils are so chimplike that they may represent the long-lost ancestor of the chimp, not human, lineage.

The next field season, team member Yohannes Haile-Selassie found the first of more than 100 fragments that make up about half of a single skeleton of this species, including a pelvis, leg, ankle and foot bones, wrist and hand bones, a lower jaw with teeth—and a skull. But in the past 8 years no details have been published on this skeleton. Why the delay? In part because the bones are so soft and crushed that preparing them requires a Herculean effort, says White. The skull is “squished,” he says, “and the bone is so chalky that when I clean an edge it erodes, so I have to mold every one of the broken pieces to reconstruct it.” The team hopes to publish in a year or so, and White claims that the skeleton is worth the wait, calling it a “phenomenal individual” that will be the “Rosetta stone for understanding bipedalism.”

(Ann Gibbons, “In Search of the First Hominids,” Science, 295:1214-1219 (February 15, 2002).)
Of course a key feature in demonstrating that an organism was bipedal is the precise shape of its pelvis. But look at what one of the current media stories on A. ramidus is reporting about the original condition of the pelvis that was discovered:One problem is that some portions of Ardi's skeleton were found crushed nearly to smithereens and needed extensive digital reconstruction. "Tim [White] showed me pictures of the pelvis in the ground, and it looked like an Irish stew," says Walker. Indeed, looking at the evidence, different paleoanthropologists may have different interpretations of how Ardi moved or what she reveals about the last common ancestor of humans and chimps.

(Michael D. Lemonick and Andrea Dorfman, "Excavating Ardi: A New Piece for the Puzzle of Human Evolution," Time Magazine (October 1, 2009).)
The recent news report in Science recounts the same problems with the fossil:But the team’s excitement was tempered by the skeleton’s terrible condition. The bones literally crumbled when touched. White called it road kill. And parts of the skeleton had been trampled and scattered into more than 100 fragments; the skull was crushed to 4 centimeters in height.

(Ann Gibbons, "A New Kind of Ancestor: Ardipithecus Unveiled," Science, Vol. 326:36-40 (Oct. 2, 2009).)
National Geographic put it thus:After Ardi died, her remains apparently were trampled down into mud by hippos and other passing herbivores. Millions of years later, erosion brought the badly crushed and distorted bones back to the surface. They were so fragile they would turn to dust at a touch. “Chalky”? “Squished”? “Badly crushed and distorted”? “Needed extensive digital reconstruction”? After all the media hype and overblown claims about importance of Ida, forgive me for having an initial reaction of skepticism. How far would you trust a “Rosetta stone” that was initially “crushed to smithereens” and “would turn to dust at a touch”?

Claims of bipedalism often depend upon precise measurements of the angles of key bones such as the pelvis, femur, and knee-bones. But if these bones were discovered in such a crushed, squished, etc. form, determining the precise contours of these bones might become a highly subjective exercise. I’m sure they spent a lot of time on their reconstructions (and it certainly sounds like they did) but at the end of the day, it’s difficult to make solid claims about extremely unsolid bones.

Skepticism about "Ardi's" Status as a Bipedal Ancestor of Modern Humans
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.

Is "Ardi" All Washed Up?
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."

In 2009, "Ardi" came onto the missing link scene with a bang. The journal Science called her the "breakthrough of the year." So did Time Magazine. For a discussion of some of the few dissenters to the Ardi hype, see here.

But Time Magazine has started to go over the apex of the hype curve. In a May, 2010 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.
Another 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 "missing link" status, could it be that there is more than mere science driving the promotion of these missing links?