/ 16 April 2010

Bones of contention

Bones Of Contention

Academic head-butting and one-upmanship instantly erupted after last week’s announcement of the Australopithecus sediba hominid fossil find in the Cradle of Humankind, near Johannesburg.

Because of their remarkable state of preservation and apparent transitional anatomy, with archaic and advanced traits, the discovery of two partial skeletons at the Malapa cave in Gladysvale has been widely hailed as shedding new light on hominid development — and, potentially, human evolution.

Science magazine quoted eminent palaeontologist Maeve Leakey, of the National Museums of Kenya in Nairobi, as saying: “This is a really remarkable find.”

However, it also cited Tim White, palaeoanthropologist at the University of California, Berkeley, as objecting sourly that A sediba “contributes little to our understanding of human origins”. It does not elaborate.

The most detailed spoiling comes from American palaeoanthropologist Donald Johanson, discoverer of the “Lucy” skeleton in Ethiopia. Johanson has been a leading proponent of the idea that South Africa’s australopithecenes represent an evolutionary cul-de-sac, and that East Africa, where he hit paydirt in the late 1970s, is the true cradle of humanity.

With lofty condescension, he told Scientific American that the A sediba finds are “most interesting” and that the skull of the juvenile male is “refreshingly complete”.

But he brushed off the idea the Malapa fossils represent an evolutionary link between South Africa’s Australopithecus africanus and the Homo genus, saying “he would not be surprised” if they were a new Homo species that could have migrated from East Africa.

“Finding a 1,8-million-year-old Homo in South Africa is newsworthy, since previous traces have been fragmentary and controversial,” writes Johanson with seigneurial patronage.

But even in this area, his team had gone one better, unearthing a 2,33-million-year-old Homo upper jaw at Hadar, site of the Lucy discovery. This was “the oldest anatomical evidence, thus far, for our genus”.

Johanson argues that A sediba recalls a fossil creature unearthed more than 20 years ago by his researchers in Tanzania, called Olduvai Hominid 62. This was attributed to Homo “on the basis of diagnostic features in the teeth, jaws and cranium”.

Commenting on A sediba’s teeth — which he saw after being invited to inspect the fossils by their discoverer, Wits University’s Lee Berger — he says the first and second molars showed little wear, “suggesting a diet quite different from Australopithecus”. In addition, the teeth were small, like those of Homo but unlike those of australopithecines.

“We know relatively little about the origins of our own genus, thus anything found that represents early Homo is potentially of some importance,” Johanson offers by way of consolation.

“I think these finds will refocus attention on the South African fossil sites and strengthen [their] importance for a more complete understanding of the human family tree.”