Ethiopia offers rich ground for exploring the origins of humanity, and a few home-grown experts return after studying in Europe and the US, says Geoff Watts

Palaeontologist Berhane Asfaw places a foam-lined wooden box on the table, opens the lid and gingerly removes a skull. It is curiously familiar, but only from the pages of Nature . Asfaw holds the earliest known skull of our species in his hands. It is 160,000 years old.

The globe's most important treasures have tended to migrate to the world's great museums. And the scholars who find, restore and study them are drawn to the most prestigious universities. By choosing to remain at the National Museum of Ethiopia, Asfaw and his fossil charge have bucked that trend. It seems the developing world is no longer so easy to strip of its intellectual capital.

The museum itself occupies a slightly decrepit building set back from the main road in the university district of Addis Ababa. Its modest collection includes artworks, traditional costumes, archaeological bits and pieces and a few memorabilia of the Emperor Haile Selassie. Only an enthusiast would be detained here for long.

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At the end of a rough path between the museum and the construction site next door is a short fire escape leading to an unprepossessing back room.

Squeezed into it are several desks, two or three PCs, a couple of worktables and shelf upon shelf of wooden trays and boxes. They line the walls from floor to ceiling. All are packed with fossils - the very material through which we've come to understand our origins. It's like stepping into humankind's ancestral tomb.

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Asfaw sits surrounded by the booty of scores of field trips. Ethiopia's leading palaeontologist is in his fifties and has the air of a man who is happy in his work. That's not surprising: parts of Ethiopia are nothing less than a hominid fossil hunter's paradise. The country lies at the entrance to the African Rift Valley, which for millions of years was an environment conducive to life. "It was warm and full of lakes, very lush, very green," Asfaw says. For millions of years it teemed with animals, alongside which lived a succession of hominids.

The rivers that flowed into the Rift Valley carried sediments that often buried the dead, fossilising a few. Asfaw is proud to boast: "This is the only place in the world where you can find the full uninterrupted record of human evolutionary history."

The skull on the table is almost complete; only a quarter of one side of the face is missing. It was found in 1997 near a village called Herto in the Afar region of Ethiopia after being exposed by flooding. "This particular specimen was found by a graduate student who is now teaching at Stanford University," Asfaw explains.

Its owner would have looked just like us. "If you saw him fully dressed and walking in the streets of Addis Ababa, you wouldn't know he was 160,000 years old," Asfaw says. "It's these guys who went out from Africa and produced the Caucasians, the Orientals - everyone." Asfaw then opens another box. "This is a child's skull that I found myself. It was late in the afternoon. I was tired. I was walking around and I saw some bones on the surface. I picked up the first piece and thought it was hominid, but I wasn't sure. When you really want to find something, you begin to think everything you see is a hominid bone. We call that 'hominid fever'. But when I saw some other pieces, and a small premolar tooth, I was 100 per cent sure." In all he had more than 200 fragments of what amounted to a three-dimensional jigsaw. "It took me a year to clean them and put them together," he says. "But now we have an almost complete skull."

The report on this and other skulls was a Nature cover story. This was not the first time that the group's work had won pride of place. An article on a new hominid intermediate between modern man and the celebrated Lucy skeleton had made the cover of Science four years previously. Few researchers can equal such an achievement.

A colleague of Asfaw's, archaeologist Yonas Beyene, joins us. His main interest is the cultural history of early hominids, particularly the tools that they began to use about 2.6 million year ago. He is, like his friend, an internationally recognised expert.

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Asfaw and Beyene both trained abroad. Beyene's first degree was in history.

He went to France, did a PhD at the Institute of Palaeontology in Paris, followed by postdoctoral work at the University of California, Berkeley, and the University of Indiana, Bloomington. He smiles: "Then I thought it was time for me to come back." Asfaw is older than Beyene, but his experience is not dissimilar. He began studying geology in Addis Ababa but got involved in anti-government protests and spent a year in prison. He eventually finished his course and, by then with a wife and child, looked for work. "My first job was preparing a summary of Ethiopian prehistory. I found I was really fascinated," he says. But his obsession with bones developed after he won a scholarship to do a doctorate at Berkeley.

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"By the time I'd got my PhD in 1988, I had a burning desire to come back to Ethiopia," Asfaw says. He found work mapping the country's archaeological resources before a change of government prompted him to quit the country again for a while.

There is little doubt that Asfaw and Beyene could have their pick of jobs in Europe or North America. They are circumspect about offers they may have received - but some colleagues have left: Yonas Halie-Selassie, lead author of a 2001 Nature report on the earliest known fossil hominids, is now curator of physical anthropology at the Cleveland Museum of Natural History. Those who have moved abroad return to Ethiopia to do field work.

They can afford to study their country only by seeking jobs outside it.

"I never really wanted to leave Ethiopia and settle in the US," Asfaw says.

"Of course, it's attractive. You get paid a lot. You can fulfil your desires. But my desire was to find new fossils and do research." Beyene, too, has resisted the temptations. "I'm very happy to remain here in Ethiopia. If you are interested in prehistory, this is where to work. It's a blessing to be born in place where you have the raw materials to study."

"Like the waterfalls, the lakes and the rivers, these fossils are the treasures of the country," Asfaw declares. "If you think of all the different animals that used to live in the Rift Valley, and how lush it was with all the lakes and the rivers, then I think that area may be described as a Garden of Eden."

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And he has no intention of being tempted away from it.