Three years old – give or take three million

[OpenMind]

http://www.telegraph.co.uk/news/main.jh ... w_21092006





Also reported here:

http://www.nytimes.com/2006/09/21/scien ... ?th&emc=th



Three years old – give or take three million

By Roger Highfield, Science Editor

(Filed: 21/09/2006)

The skeleton of a little girl who died three million years ago could shed new light on human evolution, scientists say today.

The small bundle of bones from what is now a desert in northern Ethiopia has been nicknamed Selam (peace) by her discoverers and represents the most complete ancient infant of this geological age, estimated to be about three years old when she drowned.



The unprecedented discovery opens many new avenues for efforts to understand the childhood of our early ancestors. Selam's bones suggest she walked upright but may have been good at climbing trees as well.

She had a hyoid or tongue bone, only found before in Neanderthals of all other ancient humans, a find that will trigger debate about whether she sounded like us or more like an ape.

The bones were found entombed in a slab of sandstone in the Afar region, a remote part of the Dikika desert, by Zeresenay Alemseged, an Ethiopian paleoanthropologist, and are unveiled today in the journal Nature.

"This is something you find once in a lifetime," says Mr Zeresanay of the Max Planck Institute for Evolutionary Anthropology in Leipzig.

To date, skeletons of infants as complete as the Dikika girl represent only recent members of the human evolutionary tree, such as Neanderthals and modern humans, which date from hundreds of thousands of years ago.

Not a single young child was known from the preceding several million years by more than a piece of skull, jaw or a few teeth.

The Dikika skeleton, dated to 3.3 million years ago by Dr Jonathan Wynn, of St Andrews University, and colleagues, is the best preserved fossil of her species, Australopithecus afarensis.

That is the same species as the superstar fossil called Lucy, a 3.2 million-year-old adult female discovered nearby in 1974.

Unlike Lucy, Selam has fingers, a foot and a complete torso. "But the most impressive difference between them is that this baby has a face," says Mr Zeresenay.

From the waist down, Dikika girl looked like us. One of her human-like knees was complete with a kneecap no bigger than a pea. The angle of her femur from knee to hip is close to that of a modern human, implying she walked efficiently on two legs.

But her upper body, like Lucy's, had ape-like features. Little Selam had surprisingly gorilla-like arms and shoulder blades. Her brain was small, her nose flat like a chimpanzee's, and her face long and projecting.

Her finger bones were curved and almost as long as a chimp's.

Prof Maciej Henneberg, of Adelaide University, said the discovery was consistent with "hand supported bipedalism" in which Selam walked upright but supported herself by holding on to low branches.

"We humans still like to do it by holding a handrail when climbing the stairs or standing on a bus or suburban train.

"Lucy and her tribe may have lived in an environment offering hand holds for upright walking — trees too small to climb, yet tall and strong enough to provide hand grip."

Mr Zeresenay first led a band of fossil hunters into the badlands of the Afar depression in 1999 but it was only at the end of the next year that they found Selam, after enduring extreme heat, flash floods, malaria, wild beasts and shoot-outs between feuding ethnic groups.

On Dec 10, 2000, Tilahun Gebreselassie, an expedition member, was the first to see the tiny face peering from a dusty slope, as Mr Zeresenay worked nearby. Not only was the child's skull in perfect shape, but tucked beneath in a hard ball of sandstone were many upper body bones.

The cause of death was not evident, though the Awash River had buried the body in pebbles and sand in a flood that possibly killed her.

Etching away sandstone with a dentist's drill, Mr Zeresenay has gradually revealed her anatomy — a full set of both milk teeth and unerupted adult teeth, tiny ribs positioned along a sinuous spinal column and one finger curled in a tiny grasp.

Where her throat once was lay a rare example of a hyoid bone, offering an early glimpse of the evolution of the voice box because it is between that of modern people and apes.

Prof Colin Groves, of the Australian National University, said: "This is interesting because it is more like that of gorillas and chimps and suggests that the vocalisations were loud and forthright."

With the entire brain cast "we can now examine whether our earliest ancestors grew their brains in the uniquely human way", said Prof Fred Spoor, a co-author, of University College London.

"This at a time of human evolution when they looked a good deal more like bipedal chimpanzees than like us."

Selam's brain is estimated at 330cc, which is not very different from that of a similarly aged chimpanzee.

However, Dikika girl had formed as little as 63 per cent of the adult brain size, slow for a chimpanzee but closer to humans.

At some point bipedal humans lost the opposable big toes of chimpanzees and other apes, which baby chimps use to grip their mothers with their hands and feet. This allows her to forage, escape danger, and travel while keeping her baby close.

But Dikika girl's big toe — the first ever found in an A. afarensis fossil — is still locked in sandstone.

If it shows that A. afarensis babies lacked opposable big toes, that means the little hominin probably had to be carried, limiting the mother's ability to care for herself.

She might have depended on the larger group for food and protection, thus strengthening social bonds.

The work was funded by the National Geographic Society, the Institute of Human Origins, the Leakey Foundation and the Max Planck Institute.

Dr Charles Lockwood, of University College London, said: "It's impossible to overstate the importance of this specimen".

Prof Peter Brown, of New England University, called it "a truly amazing discovery".

© Copyright of Telegraph Group Limited 2006.