Is the 7-million-year-old Toumai skull the earliest example of mankind? Palaeontologist Michel Brunet made headlines when he said it was - but not all his colleagues agree. Jane Marshall reports

Michel Brunet was already overstretched last week, commuting like a shuttlecock between Paris and his base in Poitiers for conferences, lectures, events for the national F¨ºte de la Science and meetings with people from the prime minister down. But the French palaeontologist was also having to face the fallout from assertions that his greatest discovery, Touma?, a fossilised skull some 7 million years old, was not, after all, mankind's oldest known ancestor.

Four colleagues had claimed the skull of Sahelanthropus tchadensis - which Brunet's team recovered last year with fragments from at least five different individuals in the Djurab desert of northern Chad - was more likely to be a female gorilla than a hominid.

Last July, the scientific journal Nature published a paper by Brunet, anonymously peer reviewed by five independent experts, proclaiming the skull was from "the earliest known hominid".

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But this month in Nature's "brief communications" section there is a damning article signed by Milford H. Wolpoff of Michigan University, Brigitte Senut of France's national Natural History Museum, Martin Pickford of the Coll ge de France and John Hawks of Wisconsin University. They pick Brunet's paper apart, claiming that Toumai displayed features "that link the specimen with chimpanzees, gorillas or both, to the exclusion of hominids". They conclude: "We believe that Sahelanthropus was an ape."

Their piece is accompanied by a detailed rebuttal by Brunet, who points out that dissenters in the 1920s also said that the discovery of the first early hominid, Australopithecus africanus , by Raymond Dart in South Africa, was a juvenile gorilla. Those sceptics later admitted their error.

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Last week Brunet was in positive mood. "It is important to know that two of the 'brief communications' authors have not even seen Toumai, and the others (Senut and Pickford) have seen it only for a few minutes," he says. "Natural sciences are sciences of observation. I am surprised that half the detractors speak of fossils they have not seen, and the other half are those who published (data on) the hominid that was until then the oldest."

Until Toumai came along, Senut and Pickford's discovery of Orrorin, dated at 6 million years and recovered in Kenya, was claimed to be the oldest-known hominid.

"To define a natural group, a species, a genre, a family, there must be at least one derived feature that is specific to this group, that belongs only to this group. Ancestral features are not significant. Wolpoff et al have not proposed a single derived feature to demonstrate what they claim," Brunet says. "Therefore, the conclusion is that, if they claim Toumai is a gorilla, they should identify a derived feature shared by Toumai and a gorilla and publish that in an international peer-reviewed journal."

Brunet spoke as we travelled from Paris to Poitiers, the town in western France where Brunet is a university professor, director of the geobiology, biochronology and human palaeontology laboratory of the faculty of sciences, and head of the National Centre for Scientific Research's mixed research unit 6046.

An imposing man with a trim white beard, Brunet links his choice of career "completely" to his childhood. Now in his early 60s, he was born at his grandparents' farm in the country during the second world war. Brunet lived with his grandparents in the wilds of the Vienne department in west-central France until he was seven, without attending school. "That was something I negotiated with my grandmother," he says.

By the time he went to live with his parents in Versailles he had a lasting passion for nature and life outdoors. "I can't stay a long time in a big building. I was interested in biology and animals. I thought of doing medicine, but it would have meant being closed in a hospital. At the time there was no flying-doctor service, or M¨¦decins sans Fronti¨¨res. If there had been, I would have done that."

In the mid-1960s he followed his first doctorate in palaeontology from the Sorbonne, with another in natural sciences from Poitiers University.

He worked in France and Spain; then from 1976 in Afghanistan, where he found himself in Kabul during the bloody 1978 coup. He moved to Pakistan, then Iraq "to where the Kurds live, very pleasant people. When I saw the site of Babylon I understood for the first time it was a city state - extraordinary." He worked in Vietnam and in Kazakhstan, "went to look in the craters" of Easter Island and taught in Tahiti. He also worked in the Arizona desert. "I am always attracted by deserts," he says.

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That is just as well. After Cameroon and Niger, he arrived in Chad in 1994, working in a desert half the size of France. He set up the Franco-Chad Palaeoanthropological Mission (MPFT) - a scientific collaboration between the universities of Poitiers and N'Djamena, and the Centre National d'Appui a la Recherche, based in the Chad capital. The mission's main research focuses on the origins and history of the first hominids and their environment.

Brunet's MPFT team consists of 45 scientists from ten countries and includes specialists in fossil mammals, fish, vegetation and the environment. About ten are preparing for, or have obtained, their PhDs. Brunet deliberately included Chadians in the team, persuading France's foreign affairs ministry to fund scholarships. Mackaye Hassane Ta?sso became the first Chadian to gain a PhD in palaeontology in 2001; Likius Andossa will become the second in December. N'Djamena University now has a fledgling palaeontology department and has recently opened a fossil research centre.

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Ahounta Djimdoumalbaye, the Chadian student who unearthed Touma?, is due to arrive in Poitiers this week to start studying for a masters degree.

The team visits Chad once or twice a year, between October and March. "Otherwise it is too hot," says Patrick Vignaud, lecturer and researcher at Poitiers, who co-signed Brunet's Touma? article in Nature . "Everything must be transported from N'Djamena, which takes three days by vehicle. Food is three kinds of vegetables, potatoes, rice, pasta, fish and bully-beef, everything canned, and we drink bottled water. It's important to have good psychological and physical strength. You are isolated from everything, including your family."

It can be particularly hard to deal with the harsh wind and sandstorms, but though "they handicap our conditions of work, they are also an advantage because they strip the surface, and then you can find fossils," Andossa says.

Since 1994, the team has found more than 10,000 vertebrate remains, with 42 fauna species from Touma?'s era, estimated at nearer 7 million than 6 million years ago.

Before Touma?, the high spot in Brunet's career was the 1995 discovery at another Chad site of "Abel", Australopithecus bahrelghazali , a 3-million-year-old hominid Brunet named after his friend Abel Brillanceau who died from malaria in 1989. Abel was the first proto-human found west of the Rift Valley that cuts down through the middle of eastern Africa - previously all early hominid traces had been located in East or South Africa, giving rise to the "East Side Story" theory that man originated in East Africa.

But with the discovery of Touma?, Brunet says: "We have widened the cradle of our origins."

Brunet admits he can be "aggressive", but says that is because for him his work is the most important thing - "not getting involved in polemics" with colleagues in what he calls "the hominid fever that is affecting everyone at the moment".

"It is like a game at primary school. We're still kids. We play at finding the oldest fossil, but if we are scientists we must admit that we can't always win - or always lose," he says. "Science is about finding something new, and if we can't accept that, we shouldn't play.

"Today's truth is not necessarily tomorrow's, and not necessarily yesterday's; that is science," he says.

He is also scathing about "armchair anthropologists", who hypothesise without doing their own research in the field. "There are many scientists who speak without having seen for themselves," he says.

Even off site, his schedule is punishing. On just one day in Poitiers last week, he combined his laboratory work with a planning meeting at the Pierre-Mendes-France scientific and cultural centre, of which he is vice-chairman, to discuss a Touma? exhibition that will tour France and abroad. He rounded off the day with a packed public lecture.

This week he is in Zurich organising a reconstruction of the Toumai skull. Then he is off to the US. In between, he is preparing for his next Chad expedition. The aim is to find limbs and other fragments that will give more clues to Touma?'s identity, he says.

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