Maybe Lucy wasn't your mom: Paleo-anthropologist finds himself in a three-million-year-old argument

Anthropology is notorious for its bare-knuckle style of academic brawling, and Duke's Steve Churchill finds himself at the center of what might be a very loud and protracted fight over human evolution's past.

Churchill of Duke's department of evolutionary anthropology is part of an international team of scientists describing features of a pair of 1.98 million year old fossil proto-humans discovered in a South African cave in 2008. The scientists have written seven papers appearing in the April 12, 2013 edition of Science. There were six earlier papers in September 2011 and two before that in 2010.

They've named this a new species: Australopithecus sediba, though of course there's been some argument about that.

The leader of the team, Lee Berger of the University of Witwatersrand in Johannesburg, has become something of a lightning rod for declaring Sediba a better candidate to be the ancestor of our genus—Homo—than any other hominin specimens found to date.

This has all been a bit upsetting for a large and powerful tribe of anthropologists who have dubbed Australopithecus afarensis—the famous 3.2 million year old "Lucy" of East Africa—as the proper progenitor of Homo sapiens.

Found together in a small cave called Malapa less than an hour outside Johannesburg, the adolescent male and adult female that comprise Sediba are unusually complete. They and all the animals preserved around them were fixed in anatomical orientations that show how the bones related to one another when their flesh was whole.

The Sediba male's skull was so complete and well-protected by the matrix of earth that sophisticated imaging had to be used to map the brain cases from the inside. (Their brains weren't very big.) CT Scans and 3D printing have been used to create other casts of the fossils for study.

It's good data, and a lot of it, in a field where entire papers have been written about a single tooth or a wrist bone.

Churchill is confident that this latest round of analyses and the spectacular amount of information still to be extracted from the cave will bolster Sediba's claim, bit by bit. "But this is all going to be controversial," he says.

An ape in transition

The 2013 papers examine how Sediba walked, climbed and chewed, and they build on the emerging picture of a "mosaic" creature—part ape, part recognizably human.

The torso is cone-shaped and narrower at the shoulders like an ape. This is a climbing chest, not an arm-swinging, bipedal walking chest like ours that is cylindrical and wider at the top, Churchill says.

The arms, in an analysis that Churchill led, were found to be well-suited for climbing. "It's a pretty apey scapula," Churchill says, fishing a cast of Sediba's shoulder blade out from beneath his computer monitor. But these arms also end in a hand that was capable of a tool-maker's "precision grip."

The spine, though familiarly curved for upright walking and having the same number of lumbar vertebrae as ours, is more flexible in its lower reaches than a modern human's. Monkeys are long and flexible in the lower back; chimps, gorillas and humans are not. "We're not sure what this is telling us," Churchill says.

The leg is for bipedal walking, but not in a way we've seen before. This analysis, which Jeremy DeSilva of Boston University led, suggests that the weight of each Sediba footfall was born along the outside of the foot, rolling toward the ball and resulting in a different gait from our own. The middle of Sediba's foot is more flexible than ours, which is another tree-friendly feature, Churchill says.

Afarensis footprints found in East Africa and dated to 3.6 million years show a gait more like ours, but their feet are different both from ours and Sediba's. So now there are different forms of bipedal walking in the human and pre-human record. "It looks like the earlier hominins weren't perfected bipeds," Churchill says.

It looks like upright walking may have evolved more than once, which is what one would expect from the way evolution generally works.

And based on the pronation of this foot, "I think it's unlikely that Lucy is ancestral to Sediba," Churchill says.

And now the gloves really come off.

In a paper about the shapes of the teeth, a team led by Joel Irish from Liverpool John Moores University (LJMU), found that Sebida's teeth are more similar to its fellow South African species, Australopithecus africanus and the species of Homo that came later than they are to Lucy. In an official statement, LJMU says "This surprising result … alludes to the possibility that Au. sediba, and perhaps Au. africanus are not descendant from the east African australopiths, such as Au. afarensis."

Time will tell

Churchill expects the arguments will come from all corners about ways in which the Sediba team may have misinterpreted their data. But the team and Wits University have been very forthcoming in providing other researchers with casts of the specimens and team members have taken the casts along to conferences for show and tell.

There are a lot more features of these two specimens to be analyzed and more Sediba individuals to be extracted from the cave. This will last for many more years.

Time—and a lot more papers—will tell, Churchill says.

"A lot of what we think about human evolution comes back to the order in which the specimens were found and the ideas that were built around them," Churchill says. Lucy was found in 1974.

Sediba has only had five years to fight for its space on the family tree.

Provided by Duke University