Chad, Cradle of Humanity ?

These exceptional fossils of the origins of man were collected in the Borkou, erg of Djourab, Sahara of Chad

Time july 22, 2002. Cover of the Europe, Middle East, Africa edition

Given the harsh conditions that exist today at the excavation site, a place called Toros- Menalla, it's a wonder that the fossil was found at all. This brutally hot, dune-spattered landscape lies in the middle of the Djurab Desert, about four days' drive north of N'Djamena, the capital of Chad. Rusting pieces of battle tanks are scattered all about, leftovers from 30 years of civil unrest. Windstorms blow up frequently, sandblasting everything in sight —including the scientists, who have to seek refuge inside their tents for days at a time. "They really are the most unimaginable field conditions," says Harvard paleontologist David Pilbeam, who has worked with Brunet.

DOZENS OF SPECTACULAR FOSSILS OF HUMAN ANCESTORS had previously been discovered in the Great Rift Valley, part of which slices from the Red Sea through Ethiopia, Kenya, Uganda and Tanzania, but Brunet had reasons to suspect that Chad could also be fruitful. For one thing, the area around Lake Chad had already yielded a rich trove of primitive vertebrate fossils. For another, he knew that the Rift Valley's paleontological track record did not actually prove that humanity had arisen only there. And there was a nice practical advantage as well. As a Frenchman, Brunet was especially well equipped by language and history to work in a former French imperial outpost like Chad.
In the Rift Valley, to the east, torrential downpours erode the jagged hillsides and bring ancient fossils to the surface. In the Djurab, Brunet and his colleagues realized, the relentless winds would have a similar erosive effect. So, accompanied by some 40 scientists from 10 countries, Brunet's Franco-Chadian Paleontological Mission began to dig in the Djurab in 1994.

It didn't take long for it to become clear that his reasoning was dead on. To date, the team has found 10,000 fossils in the area, including those of all sorts of animals and, seven years ago, at least one ancient hominid—a 3.5 million-year-old jaw that some researchers believe may come from the same species as Lucy (though Brunet has other ideas). Then, on July 19 of last year, a student named Ahounta Djimdoumalbaye unearthed the astonishing skull. "He is by far our best fossil hunter," says Brunet. "[Our colleague] Patrick Vignaud and I said to him that he would be the one to make a huge discovery."

The cranium was somewhat squashed, and blowing sand had eroded some of its detail, but it was nearly complete. And in a game where an entire jawbone is regarded as a rare treasure, the fossil was almost a miracle. Over the next seven months, the team found pieces of what it believes are at least five individuals of the same species, including two lower-jaw fragments and three isolated teeth. Without a telltale foot, leg or other skeletal feature, the team could not be positive that the animal walked upright, but its skull is similar in important ways to those of hominids that did.

Ideally, the researchers would have preferred to find the bones sandwiched between layers of volcanic ash containing potassium and argon, as these can be precisely dated by tests involving radioactive decay. Unfortunately, the geology at Toros-Menalla did not cooperate. But the scientists found something nearly as good. The site was replete with fossils from all sorts of other primitive animals, including fish, crocodiles, rodents, elephants, giraffes, aardvarks and more--42 types in all. Many were identical to specimens that have been radiometrically dated with great precision elsewhere. As a result, a team led by Vignaud confidently pinpointed the skull's age at between 6 million and 7 million years, probably much closer to the latter.

That puts the new Sahelanthropus tchadensis at a crucial evolutionary crossroads. Scientists have long believed that apes and humans share a common ancestor. But recently, comparisons of fossil and modern primates and analyses of modern ape and modern human dna have independently indicated that a single ancestral ape gave rise to both chimps and hominids between 5 million and 7 million years ago. That presumed great-great-great- grandape almost certainly swung from trees in the African forest. If so, then Sahelanthropus, or Toumai, could well have been the very first hominid, or at least one of the first, to begin the evolutionary march that ultimately led to Homo sapiens.
But in the contentious field of human paleontology, "could well have been" leaves plenty of room for heated argument. There seems little doubt, at least, that Toumai was truly a hominid. Though the skull and brain are no bigger than a chimp's, that is no surprise. Our characteristically large brains did not evolve until about 2 million years ago, well after Lucy's time. But features like a short face with a massive brow ridge, a mouth and jaw that protrude less than in most apes, and relatively small canine teeth make it clear that this creature was not a chimpanzee.

Where exactly Toumai falls in the evolutionary scheme of things, though, depends largely on whom you ask. A number of distinguished paleontologists, including Bernard Wood, Ian Tattersall of the American Museum of Natural History in New York City, and Chris Stringer of London's Natural History Museum, perceive the face to be jarringly modern— more modern even than Lucy's species, Australopithecus afarensis, which is between 3.6 million and 2.9 million years old—and thus quite different from what they expected to see in such an ancient hominid.

OVER THE YEARS SINCE LUCY WAS FOUNDS, several even older hominids, including Ardipithecus ramidus ramidus (4.4 million years old) and Ardipithecus ramidus kadabba (5.8 million), have been put forward as the most ancient of our direct ancestors. But Toumai is older still. If it is as modern looking as Wood believes, Lucy and the others may not be our direct ancestors at all but instead dead-end side branches of the family tree, like the Neanderthals. That would make them not our great-great-great-grandparents but rather ancient uncles and aunts whose lineages have long since gone extinct. One possibility is that Sahelanthropus gave rise to intermediate descendant species that have not yet been discovered. These descendants would have led to Homo habilis or Homo rudolfensis, both of which are contenders for the first member of our genus, which arose about 2 million years ago.
If so, this lends support to an evolutionary scheme that has been gaining scientific support. Instead of a tree, with a main trunk and a few side branches, hominid evolution is now viewed more as an overgrown bush, lush at every point with multiple competing species. The evidence certainly seems to point that way. Over the past couple of decades, anthropologists have been finding more and more hominid species dating all the way from hundreds of thousands to millions of years ago, many of them overlapping in time. During most of our ancestors' history, it appears, multiple species of humanlike creatures walked the earth at once.
That really should not be surprising. Most types of animals—monkeys, whales, cats, apes—come in multiple varieties. As recently as 30,000 or 40,000 years ago, when Homo sapiens was sufficiently evolved to make jewelry and paint hauntingly evocative drawings on cave walls, we shared the planet with a second hominid species, the Neanderthals. And although it seems natural to us that only one species of hominid lives today, it is in fact an exception to nature's way of doing things.

But if multiple hominid species have been the rule all along, there is no reason to think this wasn't the case right from the beginning. Evolution provides plenty of examples in which new types of animals emerge not just as single species but as collections of similar species that share many but not all physical attributes. The rich diversity of finches that Charles Darwin discovered in the Galapagos Islands is perhaps the most famous example.
According to many anthropologists, Brunet's discovery supports the idea that evolutionary diversity was true for hominids as well. "My guess," Wood offers, "is that Sahelanthropus is the first of what will turn out to be a whole handful of apes and apelike creatures living throughout Africa 6 or 7 million years ago." In this bushy model of evolution, even a remarkably modern face might not guarantee that Brunet's new hominid was a direct ancestor of modern humans. Maybe it was just one of several modern-looking hominids that arose at about the same time.

Or maybe all these learned experts are barking up the wrong evolutionary tree after all. At least one equally eminent paleontologist, Tim White of the University of California, Berkeley, disputes the assertion that Toumai derails the standard evolutionary family tree, let alone plants a bush in its place. The discovery is a tremendous accomplishment, he says. "This fossil is the closest we've got to the common ancestor. But dentally, it's just like Ardipithecus, except for a few minor characteristics." The mix of primitive and more advanced traits leaves him similarly unimpressed, since such mixing has been seen in various species discovered over the past 80 years. In spite of what his colleagues say, White believes that Toumai may well be the direct ancestor of all later hominids, Lucy and ourselves included.

If the new hominid does eventually upend the conventional wisdom, however, it will raise all sorts of questions. For example, if Sahelanthropus had descendant species that gave rise to H. habilis, asks Harvard's Lieberman, where are they? Nobody knows, moreover, what triggered the emergence of the earliest hominids in the first place. Virtually everyone now agrees that walking upright was the key physical adaptation that set the hominid line in motion. But that adaptation had to have some evolutionary advantage for it to persist. What, exactly, was so great about walking on two legs?
A decade ago, the leading theory suggested that climate change had dried Africa out, replacing the forests, where apes thrived, with grasslands. A walking ape would be better suited to this environment, since tree climbing would be useless. Standing would give a better view over the top of the grasses of potential enemies. Also, a vertical position would offer less exposure to the harsh rays of the sun.
That all made sense until field scientists, including White, began finding early hominids who lived in partly wooded places, not pure savanna. As deduced from the sorts of animals Brunet found at Toros-Menalla, that seems to be the kind of environment Sahelanthropus inhabited as well. With the simple climate theory already on the way out, paleontologists have come up with other ideas. They now believe that woods survived in the changed climate but were probably interspersed with patches of savanna—precisely the setting in which Brunet found Toumai.

An ape walking on two legs could traverse these open expanses, much as the earlier theory contended, to get to a safe and comfortable habitat in the next forest over. With its free hands, the ape could carry extra food—very useful when crossing expanses where fruit might not be available for the plucking. Free hands might also be useful for sex, although not in the way you might think. The best male upright walkers could bring back food for the females of their species, increasing their chances of winning a mate and passing on their genes—or so suggests C. Owen Lovejoy of Ohio's Kent State University, the leading proponent of this theory.

AS FOR THE POPULAR PERCEPTION that human evolution began in East Africa —well, on reflection, that was never as convincing as it was made out to be. Even those who leaned toward that view knew intellectually that a few dozen individuals from a few sites spaced over millions of years constituted a pretty slim line of evidence. After all, even a shambling, apelike hominid could range a few thousand miles—from Chad, say—in a mere generation or two. The fact that so very few hominid fossils have been found, even in East Africa, makes it clear how rarely these ancient bones survived. "If you think of Africa as a giant place where human ancestors existed for the past 7 million years," says Berkeley's White, "you have to get lucky to find places where environmental conditions allowed them to live and where the geological conditions allowed them to be preserved."
But that also means that paleontologists could get lucky in many more places than they have looked so far. White and other old East Africa hands will continue the excavations they have under way in those traditionally fertile fossil fields. Other, less established scientists, though, may now feel emboldened to look in other parts of Africa with greater confidence that there is something important to find.

Brunet, meanwhile, has every reason to keep mining the windswept desert of Chad. "There's still plenty of work to do," he says. He and his team will be looking not only for additional Sahelanthropus bones but also for even older sediments that are between 7.5 million and 10 million years old—rocks that could yield the ancestral species that gave rise to both humans and chimps. Paleontologists often take months or years to announce the existence of discoveries they have in hand, so it is quite possible that he and his team have already found something more.

Indeed, the last sentence of their paper in Nature declares that while Sahelanthropus will be central to illuminating the earliest chapter in evolutionary history, "more surprises can be expected." Given the splash Toumai has made, that could prove to be an understatement.

With reporting by Delphine Schrank/Poitiers

Time, July 22, 2002, Father of us all ? p. 46-53

Or maybe it's not our ancestor at all, but some star-crossed evolutionary line that was far ahead of its time. While paleontologists agree that chimps and Homo sapiens share a common ancestor, there's debate on just how straight the path was from that ancestor to humans. Instead of the transformation illustrated in 1950s textbooks, with a neat progression of chimp to stoop-shouldered caveman to Tony Curtis, many paleontologists believe prehumans emerged in a number of different lines, with all but ours dying out. By this view the way to chart human evolution is not by a tree but a complex bush. "Maybe [Toumai] is an indication that there were lots of different species of hominid that were reproductively isolated," says Don Johanson, a "bushy" theorist who discovered the 3 million-year-old "Lucy" bones in 1974. "They all went in their own directions.
By this theory, previous celebrated finds like Lucy (who walked upright but had a chimplike snout) or the 2 million-year-old Homo habilis (strong brow ridges and a flat face) can't ever be placed in a serial progression, but were all candidates in the ultimate game of "Survivor." Not everybody buys into this bushy theory. "It's 'X-Files' paleontology" with no supporting evidence, says fossil hunter Tim White of the University of California, Berkeley.
In any case, Brunet's amazing find gives us plenty to consider. The skull is nearly complete--itself something of a miracle. Although Toumai's brain was about the size of a modern-day chimpanzee's, its face is quite flat, a classically human trait. Unlike chimps, it sports a large brow and small canines. And even though Brunet's team found no signs of a skeleton, the way the spine connects to the skull leads scientists to think that Toumai may have walked on two feet.
There is one question the Toumai skull does settle. You can stick a fork in the theory that human ancestors loitered in eastern Africa until the last couple million years or so. This "East Side Story" held that prehumans arose after tectonic forces formed the Rift Valley 8 million years ago. While chimps on the western side were fat and happy in their lush forests, their hapless brethren were subjected to an increasingly harsh, dry climate, forcing them to evolve. Toumai shows that the Rift Valley had little to do with how and why hominids evolved. It also means that scientists have to roll back their estimate of when chimps and humans diverged by at least a million years.
For more than 20 years, the 61-year-old Brunet has defied conventional wisdom in seeking hominid fossils in all the supposedly wrong places. After false starts in Pakistan and Cameroon, he settled on Chad. Though now as flat as a dot-com's revenues, millions of years ago the Djourab desert was a huge basin surrounding a freshwater lake teeming with now extinct fish and amphibious mammals. Nearby, creatures vaguely resembling today's giraffes and pigs grazed on grasses and leaves. Just the kind of place prehumans would have loved--if any ever lived there. Brunet believed fervently that they did. "East Side Story said savannah made man," Brunet told NEWSWEEK. "But the oldest are associated with forest fauna."
When Brunet arrived on the scene in 1994, he encountered sand dunes drifting across a hard desert floor, with fossils inlaid like some kind of prehistoric floor tile. One of the richest was TM266, which he explored in 1997--and figured that four years later, the shifting sands might uncover more. Talk about hitting paydirt. "Brunet's work is like looking for a needle in a hundred haystacks," says Jacques Corgin, the French ambassador to Chad. "To find what they found, you need la baraka [luck]."
Oddly, it was not until September, two months after his team uncovered the skull, that Brunet himself first laid eyes on Toumai. After his team had unearthed the skull, they wrapped it carefully in toilet paper and headed home. After three days they reached Chad's capital, N'Djamena, and phoned Brunet. The find quickly became the talk of N'Djamena, and the French press caught wind of it. The leak so infuriated the control-freak Brunet that he stayed away for weeks. Ultimately, of course, he had to venture to Chad to take plaster casts (Toumai itself will remain in his native country), and begin to address the controversy that a 7 million-year-old hunk of bone generates. But Brunet, with characteristic confidence, claims "no doubt" that his discovery is one of humanity's ancestors, "the oldest human known to now." To confirm this--and resolve some of the increasing mysteries that the residue of a 7 million-year-old creature has stirred--will indeed require la baraka.

With CHRIS DICKEY and MARIS VALLA in Poitiers and MARY CARMICHAEL in New York

Newsweek July 22 / July 29, 2002, All in the FAMILY, p. 72-75

In the French press and french version

Le Figaro, July 31, 2001 : 'Chad, craddle of humanity ?'

Le Figaro, July 11. 2002, p. 10 : 'The Oldest Ancestor of the Man is Chadian' ; 'The Djourab by 58°C without shade'

Le Figaro, 11 July 11, 2002, p. 11 : 'new grandfather or old cousin' ; 'storm under a skull'

Le Monde, July 12,  2002  : "In chad, the remains of a skull upsets the origins of man".