THREE fossil skulls from Ethiopia have turned out to be the oldest human remains ever found. Anthropologists say the 160,000-year-old bones plug a crucial gap in the fossil record around the time that our species first appeared, and give dramatic insights into the lifestyles of the earliest human beings.
The fossils suggest that the first Homo sapiens ate the bone marrow of hippos, and ritually carried the bones of their ancestors. They are also a dramatic boost to the theory that modern humans evolved in Africa and subsequently spread across the rest of the globe, according to Chris Stringer of London鈥檚 Natural History Museum, who calls them 鈥渓andmark finds in unravelling our origins鈥�.
News of the fossils鈥� age follows a detailed analysis of the remains, which were found by Tim White of the University of California at Berkeley and his team in 1997 near the village of Herto, 230 kilometres north-east of Addis Ababa (see Map). White first stumbled across a fossilised hippo skull protruding from the ground, but the team eventually recovered skull fragments from 10 humans. The site was also littered with stone tools and animal remains.
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White鈥檚 team dated the human fossils with enormous precision using a technique based on the radioactive decay of potassium into argon. When volcanic material is heated it expels argon, but on cooling the gas starts accumulating again in pockets between crystals. By analysing the gas in volcanic debris that settled with the fossils as they formed, the team could fix them between 160,000 and 154,000 years old. This makes them crucial to the debate about where modern humans evolved (see 鈥淲here, when and how?鈥�).
The prominent 鈥淥ut of Africa鈥� theory suggests modern humans evolved roughly 100,000 to 200,000 years ago in Africa, then migrated all over the Old World. But there have not been any convincing African human fossils from the time they supposedly appeared. 鈥淭he problem with the African record is that it has been really sketchy,鈥� says White. Now, in a coup for the Out of Africa theory, the Herto fossils place modern-looking humans in the right place at the right time.
White鈥檚 team painstakingly restored large parts of the skulls of three individuals 鈥� two men and a child. More than 200 fragments of the child鈥檚 skull were strewn over an area of about 400 square metres. It took two years to piece the fragments together, using clues like the impressions made by blood vessels.
The fossils look almost human, but not quite. The skulls have a longer brain case (from front to back) than human skulls, a deeper face and more pronounced brow ridges (Nature, vol 423, p 737). So the team have given these people their own subspecies, Homo sapiens id脿ltu. The subspecies name means 鈥渆lder鈥� in the language of the Afar people who now live in the Herto region. The skulls are also very large by human standards, suggesting that the adults were hefty individuals. 鈥淭hey鈥檇 be a star choice for a rugby player. You鈥檇 want them on your team,鈥� says White.
The animal fossils near the human remains give intriguing insights into the Herto people鈥檚 lifestyles. Their African habitat was a warm tropical plain near a shallow freshwater lake, teeming with hippos, crocodiles and catfish. The hippo remains suggest the people ate the animals鈥� bone marrow, as the limb bones were deliberately broken. One hippo skull had a gash 10 centimetres long made by a stone tool.
There are also marks on the human skulls. One of the two adult skulls bears parallel grooves carved by a stone tool. This doesn鈥檛 seem to signal cannibalism because the grooves don鈥檛 look like the marks made by scraping meat from bones. 鈥淭here鈥檚 no meat in the places they鈥檙e finding the cut marks,鈥� adds Sally McBrearty, an expert in tone tools at the University of Connecticut in Storrs.
Marks on the child鈥檚 skull are even more puzzling. There are cut marks made by very sharp stone flakes in nooks and crannies at the base of the skull. Part of the base of the skull was broken away and the broken edges have been polished. White says this suggests that people carried the skull around 鈥� possibly as part of an ancestor-worshipping ritual 鈥� and it got smoothed and buffed up in the process. If he is right, this would be the earliest evidence of this kind of cultural trait.
