Oldest Not-quite-living human tells a little

A special issue of Science out tomorrow publishes a number of papers on the 15-year-long study of a fossil believed to be the ancestor of "Lucy" in Africa, which scientists are excited about because "Ardi" (short for Ardipithecus ramidus) gets them closer to the point 7 million years ago where humans and chimpanzees are believed to have branched off from one another:

"Ardi is the earliest and best-documented descendant of that common ancestor. But despite being "so close to the split," says White, the surprising thing is that she bears little resemblance to chimpanzees, our closest living primate relatives. The elusive common ancestor's bones have never been found, but scientists, working from the evidence available — especially analyses of Australopithecus and modern African apes — envisioned Great-Great-Grandpa to have looked most nearly like a knuckle-walking, tree-swinging ape. But "[Ardi is] not chimplike," according to White, which means that the last common ancestor probably wasn't either. "This skeleton flips our understanding of human evolution," says Kent State University anthropologist C. Owen Lovejoy, a member of the Middle Awash team. "It's clear that humans are not merely a slight modification of chimps, despite their genomic similarity."

So what does that mean? Based on Ardi's anatomy, it appears that chimpanzees may actually have evolved more than humans — in the scientific sense of having changed more over the past 7 million years or so."

That passage in the Time article was fascinating for me. Scientists have always assumed that early humans were similar to chimps and that we evolved to be able to walk upright, etc. But what if they got it backwards? What if the earliest chimps were more like humans, and *they* evolved to be tree climbers? It would suggest that humans aren't in fact the end product of natural selection after all. I can't explain it, but I think that's very cool.

"What Ardi tells us is there was this vast intermediate stage in our evolution that nobody knew about," said Owen Lovejoy, an anatomist at Kent State University in Ohio, who analyzed Ardi's bones below the neck. "It changes everything." -- quoted in National Geographic. Ardi also tells us that, unlike some people, scientists are capable of adapting when new evidence emerges.