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paleontology

Torturous routes

The oldest hominid fossil suggests that our historical evolution is more complex than we had imagined

“It’s a lot of emotion to be holding in my hand the beginning of the human lineage.” Absolutely convinced of the importance of his discovery, the French paleontologist, Michel Brunet, from Poitiers University, was sheer happiness on the 12th of July when publicly exhibiting for the first time in France, a cranium and fragments of a mandible found by his team in the Chad dessert of Central Africa after some twenty five years of excavations. With between 6 and 7 million years of age, the Sahelanthropus tchadensis or the Toumai Man – hope of life in the local tongue – is the oldest and most primitive precursor to the human species, which brings together both traces of hominids and of monkeys.

This is one of the most important finds of the last one hundred years for having lived during a critical period, in which there was the separation between hominids and monkeys and about which little is known, and as well for knocking down part of the puzzle about the evolution of Homo sapiens: instead of the so wished for linearity, the idea now being advanced is that the development of man was chaotic, with detours and obstacles, starting from the initial point, represented by a group such as the lineage that has just been discovered.

The main issue concerning the edition of Nature that began to circulate on the eve of Brunet’s presentation, Toumai doesn’t only just throw back the origin of man another 1 million years into the past – before him, the oldest ancestor was Orrorin tugenensis, discovered in 2000, with an age of 6 million years. The cranium that emerged from the sandy dessert of Chad also shows that the evolutionary process of Homo sapiens is nothing exceptional and passed through the same dramas as other species. “By far, our history is not linear”, says Hilton Silva, an anthropologist at the National Museum of Rio de Janeiro. The idea of a tree with a single branch that represents our past, has fallen apart, and in its place, a bush is growing, with branches sprouting at every moment, growing in all directions and interconnecting among themselves. As well, it is no longer possible to sustain the idea of a missing link: “The more species that are discovered, the more we see that there is not a link, but various groups between man of today and the monkeys”, Silva reminds us.

However, is has become clearer that of the five to ten hominid lineages that must have coexisted – some appeared more like the monkeys and others like future humans. “Many researchers have already suggested that there were many lineages or routes in the evolutionary history of the human being, since the majority of evolutionary processes consist of many new adaptations, of which only a few survive”, comments Eric Delson, a paleontologist with the American Natural History Museum and with the New York University in the United States. “But now we have a piece of evidence”.

Delson only hesitated to reiterate the value of the Toumai Man for the consideration that there are two relatively recent findings as yet not totally evaluated: the Ardipithecus ramidus, discovered in 1994 in Ethiopia with an age of 4.4 million years, which supposedly was not entirely a biped; and the Orrorin tugenensis, whose importance could become clearer when more preserved examples other that the current one that is only fragments of a cranium, are discovered.

Toumai exhibits an unprecedented combination – or mosaic – of primitive and advances traits: the flattened face and the canine teeth which place it close to hominids, while the cranial size would place it in the slot of a small chimpanzee. From the back, it would probably have looked like a monkey. Coming from the sands of the dessert into the hands of researchers, it has become even more important that the Australopithecus africanus, which in 1925 testified to the African origin of Homo sapiens. This is the oldest piece of the puzzle, but not the only piece: the Kenyanthropus platyops, discovered in Kenya in 1999, also combines hominid and monkey traits – the only thing being, that it lived a lot later between 3.5 and 3.2 million years ago.

The article in Nature on the 11th of July, which describes the discovery, signed by thirty eight researchers – from France, the United States, Spain, Switzerland, and Chad -, suggests that the first hominids lived spread out along East Africa some six million years ago. If Chad truly was the birthplace of humanity, the start of the human adventure moved some 2,500 kilometers and left the Rift Valley, in the east of Africa, where up until now the discoveries had concentrated themselves.

Found in the Djurab dessert in July of 2001 by Ahounta Djimdourmalbaye, a student at the Ndjamena University who had been working with the researchers, Toumai lived there when there were forests and grasslands, at the edge of a lake containing fish, amphibians and crocodiles, but not far from the sand dunes, according to the geological evidence examined in a complementary article signed by Patrick Vignaud, also from Poitiers University, and the leader of some twenty specialists. Brunet completed the main article in Nature showing that he knows the story has only just begun: “The Sahelanthropus will have a decisive role in this effort (of understanding the first chapters of the story of human evolution), but more surprises can be expected”.

In the days following the presentation of the fossil to the world, criticism came forward. The most emphatic came from Brigitte Senut, at the National Natural History Museum of Paris. “For me, we’re dealing with a primitive gorilla”, she says. “Traits such as the flattened face and the small canines are related to sex and in themselves do not define a hominid.” She reminds us that during the 60’s, species considered to be precursors of hominids, such as Kenyapithecus and Ramapithecus, were repositioned as female monkeys and left the human evolutionary tree. However, there is one incontestable point: the confirmation that one must look attentively to other different locations when one wishes to widen the frontiers of knowledge – it is for this reason that she has been working in Uganda, Kenya, Namibia and South Africa for some seventeen years.

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