"Ardi" - Humanity's Oldest Ancestor

Move Over Lucy, Ardi May Be Oldest Human Ancestor
by CHRISTOPHER JOYCE

October 1, 2009
Scientists on Thursday unveiled a fossil human ancestor dating back 4.4 million years " a creature more ancient than the famous fossil "Lucy." And, the scientists say, even more important than Lucy.

The team that discovered the fossil, called Ardipithicus ramidus, say it's the closest thing yet found to the common ancestor of both chimps and humans. That common ancestor is thought to have lived about 6 million years ago. From that animal, chimps and other apes evolved in one direction, while our own ancestors, the hominids, evolved through several forms into what we are now.

The anthropologists found the bones in Ethiopia, in a desert region called Aramis. Scientists have previously discovered a few teeth and bones of Ardipithicus, dating from 5 to 6 million years ago. But in this case, they have more than 100 bones from 36 individuals, including a partial skeleton of a female whom they've dubbed "Ardi."

The area excavated "was a time capsule with contents that nobody had ever seen before," says anthropologist Tim White, of the University of California, Berkeley, and the team co-leader.

The skull had been crushed into scores of pieces, says White. But after years of reconstruction work, White says, "what we have is a very small-brained cranium of an early female hominid that is very different from a chimpanzee."

That's critical, say Whites. "People have sort of assumed... that the last common ancestor was more or less like a chimpanzee." Ardi suggests otherwise; that in fact the earliest known hominid was a "mosaic," with some features like chimps but others like monkeys, such as the feet.

Other features are more like the more recent hominid, Lucy (Australopithecus afarensis), such as the teeth. For example, the canine teeth near the front of the mouth in both male and female Ardipithicus are much smaller than a chimp's canines.

"It's just a treasure trove of surprises," says C. Owen Lovejoy, one of the leaders of the team and an anthropologist at Kent State University. Take the small canines, he says. A chimp's big, protruding canines, especially the males', are for fighting or intimidating other males to get access to females, says Lovejoy. Small canines on Ardipithicus suggest a different social strategy.

"So females are picking males that are using some other technique to obtain reproductive success, and that technique is probably exchanging food for copulation," says Lovejoy.

White and Lovejoy say that the hand and arm bones, as well as bones from the feet and pelvis, suggest that Ardi was able to walk on two legs. But it was probably more comfortable in the trees, though it maneuvered on its palms in a way different from chimps.
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