In the Afar desert of Ethiopia, paleoanthropologists came across the 4.4 million year old skeleton of an early hominid, which they named "Ardi".
For nearly six million years, our ancestors have continuously inhabited the Middle Awash region of Ethiopia. Today, erosion is exposing their fossil bones again. The findings prove how primitive primates evolved step by step. Nowhere better to explore how we became humans.
In the Afar Desert, a person can die in many ways: By disease, lions, or the bite of a snake. He can fall off a cliff here, in the center of Ethiopia, or get into a gunfight between hostile clans.
But life in Africa is almost universally more endangered than anywhere else in the world. What is striking about the Afar region, however, is that the remains of the dead sometimes survive here for an astonishingly long time. Millions of years. A geological peculiarity contributes to this: The depression of Afar lies directly above a crack in the earth’s crust, which is getting wider and wider. Volcanoes , earthquakes and the slow accumulation of sediments – deposits of debris and dust – worked together ages ago to bury many bones. Much later, the ground folded back up, and erosion is now exposing the fossilized bones again. "Every now and then we get lucky and find what’s left of them," says paleoanthropologist Tim White of the University of California at Berkeley.
White, along with his Ethiopian colleagues Berhane Asfaw and Giday Wolde-Gabriel, leads the Middle Awash research project. The name refers to a section of the river Awash in the Afar region. In October 2009, researchers had publicized a sensation – 15 years after they found the skeleton of an early human who died 4.4 million years ago there, at a site called Aramis, about 30 kilometers north of what is now Lake Yardi.
The dead woman was female and belongs to the species Ardipithecus ramidus. That is why it was christened "Ardi" for short. The remains are more than a million years older than the skeleton of "Lucy", that world-famous woman of the already more modern species Australopithecus. From "Ardi", the researchers hope to gain new insights into a core question of evolution: What did the ancestor look like that we humans have in common with the chimpanzee??
Gallery: "Koko was able to show us what all apes are capable of."
For those who want to trace the evolution from apes through early human forms to the species that today determines the fate of the earth, there is no better place in the world than the Middle Awash. In addition to the site at Aramis, soil layers from 14 other time periods have released fossils of hominins. (That’s the biological collective term for the living and extinct members of the human lineage.) Together with the apes the hominins belong to the superior group of hominids.
Many of these sites are geographically so close together that you can literally walk through the history of human evolution within a few days. White invites me to join his team to prove this point. We plan to start at Lake Yardi in the present time and go deeper and deeper into the past from there. Step by step, species by species and feature by feature we should find less and less of what makes us human in the fossils.
Gallery: Homo naledi – One of us?
Herto: An old acquaintance
With two dozen scientists and students and six armed guards, we drive into the field. Our caravan of eleven vehicles carries food and equipment for six weeks. Carefully laid out terraced fields of corn and millet are soon followed by misty forests. The road is lined with flotsam and jetsam from contemporary history: Behind a bend lies the metal skeleton of an armored troop carrier from the Civil War of the 1990s, a little further on the name "Mussolini" is carved above a tunnel – a reference to the fact that 80 years ago the country was still occupied by Italy.
From the upper end of a steep slope we bump in serpentines down a gigantic natural staircase. It was formed by the Arabian continental plate drifting away from Africa. This began about 30 million years ago and caused the depression of Afar to slide deeper and deeper. The further we descend, the more sparse the vegetation becomes, the sun burns hotter and hotter. A hundred meters above the bottom of the depression we stop. On the southeastern horizon, behind the green ribbon of the Awash River, the highlands seem to merge with the peak of the young volcano Ayelu. Under the Ayelu the Yardi lake glitters.
Two days later we walk along its shore: White, Asfaw, Wolde-Gabriel as well as the American geologist Bill Hart and Ahamed Elema, the head of the Afar clan Bouri- Modaito. Colorful dragonflies dance around our feet. Today, as in the past, this is an ideal environment for the formation of fossils. Animals come to eat, to drink, to kill. Bones are buried in the mud and saved from decomposition. White – 58, tough and thin as a jackal – pokes with his ice pick at the carcasses of recently dead animals: in the skeleton of a catfish left behind by an eagle; in the head of a cow, covered with a leathery mask of dried meat. "A prime spot to become a fossil," he says.
On the first day, we walk the towering headland of the Bouri Peninsula. Here lies the Afar village of Herto. A boy and a girl approach us curiously with their herds of goats. The Afar practice pastoralism, and if you disregard the guns that have recently been added, they don’t live much differently today than they did 500 years ago. We walk in the heat among the softly bleating animals, feeling as if history is being turned back a little further with each step we take.
"Watch your step," Asfaw says as we approach the grassy huts of the thornbush-fenced village. Around me, erosion has exposed pieces of a fossil hippopotamus skull in the yellowish sand. Not far from here lies a teardrop-shaped stone axe about twelve centimeters long. The Afar do not make stone tools: we have reached the first window into the past.
This is the exact spot where a member of the team found the fragment of a hominid skull in November 1997. Its location was marked with a yellow flag, and the team swarmed out to search for more fragments. A short time later, the yellow flags stood like a field full of flowers, but particularly dense in one spot. Here, buried in the sandy soil, lay a remarkably complete human skull.
While the other team members dug up bones, geologist Wolde-Gabriel collected rock samples: chunks of obsidian and pumice, some as big as tennis balls. Such rocks, which the earth spews out during volcanic eruptions, are worth their weight in gold to geologists, because in many cases their age can be determined very precisely. The investigations revealed that the skull was 154.000 to 160.000 years old.
This chronological classification is of enormous importance. Geneticists have analyzed the DNA of modern humans from different geographical regions of the world and calculated from similarities and differences in the genetic material that all modern humans are descended from a population that existed 100 years ago.000 to 200.000 years ago lived in Africa. Fossils, which could secure the genetic model, gave it however hardly from this time. Until that find.
The broad male skull with its strong brow ridges proved to be the ideal face for the "out of Africa" theory. It comes from a very early modern Homo sapiens. Tim White assumes that it is even the oldest representative of our species ever found. The high, domed skull is astonishingly large: It has a volume of 1450 cubic centimeters – more than an average human today. On the other hand, the fossil’s long face and some features on the back of the skull also provide a link to older forms of the genus Homo here, about a 600.000 year old skull discovered by other explorers in 1976 on the opposite side of the Awash River, at the Bodo site.
"One thing we know about the people of Herto: they liked meat. Of hippos in particular," White says as he brushes sand from a hippo skull. Many mammal bones found here bear cut marks from stone tools. Whether humans actively hunted the animals or utilized the carcasses left by predators cannot be determined. Snail shells in the sand indicate that they probably dissected the animals on the shore of a freshwater lake that resembled the Yardi of today. Traces of fire or signs of a settlement are not to be found, however.
Judging from the size of the brain, the man of Herto was as "human" as anyone living today. But it is noticeable: His stone tools are quite advanced, but hardly differ from finds that 100.000 years older or 100.are 000 years younger.
There are also no pierced beads as on other, about 60.000 years younger African sites. Also missing are carved figures as known from the Palaeolithic in Europe, that epoch about 40 years ago.000 years ago, when man invented the art. 160.000 years is hardly more than a moment in the history of evolution – and yet, on our journey into the past here in Herto, we have already left behind us an essential characteristic of being human: the ability to innovate.
Some special bones admittedly show a characteristic that could be interpreted with all caution as a harbinger of later social behavior. They belong to a child who was about six or seven years old. cut marks on his skull show that he was carefully cleaned of flesh when the bones were still fresh. The nature of the cuts probably rules out cannibalism. It rather points to a ritual action. The surface of the youthful skull is intact, but in one place it looks polished, as if it has been taken in the hand many times. Perhaps it served as a kind of relic before someone laid it to rest here in Herto.
Daka: Already on our side
After a quick lunch we continue our walk on the other side of the village. Here the eastern slope of the Bouri ridge drops away into a sun-baked moonscape: gray sandstone, barren and bizarre, interrupted here and there by small caves. Wolde-Gabriel explains to me how the soil layers here were once tilted by geological faults and then exposed and shaped again over thousands of years by wind, water and gravity.
Then we are at another time window, the Dakanihylo or Daka layer of the Bouri Formation. These sediments are about a million years old. Here, in late December 1997, anthropologist Henry Gilbert discovered the top of a skull that erosion had partially exposed. The find, embedded in a 50 kilo sandstone block, was brought to Addis Ababa and there carefully cleaned in the museum with dentist’s drills and porcupine quills. Thereby the complete skull vault of a specimen of the species Homo erectus to the surface, unfortunately without facial bones.
The remains of a Homo erectus were first discovered in Indonesia in 1891. The species is one of the best known early humans. In body size and proportions it resembled us, the modern humans, already very much. The period in which he created his stone tools is called Acheuleen, after a known site in France, Saint Acheul.
typical are large, symmetrically shaped fist wedges. Elema picks one up: It’s a chunk of black basalt. The thick end lies well in the hand, to the edges and to the tip splinters have been chipped on all sides. It’s a cruder device than the work- witnesses I saw in Herto, but its symmetry reflects the ability to recognize a shape in a piece of rock and refine it with deliberate blows.
Walking upright and equipped with such tools, the Homo erectus probably the first hominid to leave the African continent almost two million years ago and migrated as far as Southeast Asia. In older textbooks it can still be found there under the name "Peking Man".
On the short walk from Herto over to Daka, once again a part of our humanity disappeared: several hundred cubic centimeters of gray brain matter. Daka’s brain skull has a volume of a thousand cubic centimeters – typical of Homo erectus, but much less than in early modern humans of Herto or the da- between dated, 600.000 year old skull of Bodo. In addition, the tools made by Homo erectus manufactured Acheulean tools not only 100000, but more than a million years almost the same.
For White there is nevertheless no doubt "that this species was tremendously successful. It has expanded its habitat beyond Africa. Homo erectus was already on our side of a dividing line in the evolution to man. If we now go further back into the past, we will look into a completely strange world."
Hata: The surprise
We don’t need more than a single step to do this. Below the sediments in the Daka layer there is a break in the geological sequence. Rock displacements and erosion have removed a whole period of time. All it takes is one big step – and we’ve skipped a million and a half years. We now walk across a bare plain, cut by dry riverbeds, which flickers reddish gray in the afternoon heat.
The reddish stratifications are called Hata. Back in the mid-1990s, a series of discoveries here opened the door to one of the biggest upheavals in our evolution. On bones of antelopes, horses and other mammals the characteristic cut marks of stone tools are to be recognized. With an age of two and a half million years they belong to the oldest evidence of the use of tools. "Notches on the inside of an antelope jaw, for example, show us that early humans cut out the animal’s tongue," White says. "So we know not only that they made tools, but also what for: to get food from mammalian carcasses."Because the scientists did not find the appropriate tools in the bones, whoever dissected the animal must have taken his tools with him. "These people didn’t have permanent settlements," says White. "They came and went."
But who were "they"? Only a few meters away from the mammal bones with the cut marks, a femur, some arm bones and a lower jaw fragment came to light – fossil remains of a single hominid. The femur was long; this was reminiscent of the genus Homo. But the forearm was also long; that fit to an ape. What lay there seemed to be the dream of every paleoanthropologist: the fossil evidence for the split of hominids into two evolutionary lineages.
At that time, a branch of the genus developed Australopithecus formidable jaw muscles and powerful molars – tools for biting down tough roots and other hard foods. The other branch produced hominins with smaller and smaller molars, lighter builds, longer legs and larger brains. It led – to us.
A larger brain is of course useful, but its maintenance is costly. It needs constantly calorie-rich food. This can be obtained, for example, by using animals torn by lions and breaking the bones to extract the nutritious marrow. At Hata, all that was missing to prove this assumption was a matching skull: it should be smaller than that of a Homo erectus, but clearly on the evolutionary path in its direction. Promptly, Yohannes Haile-Selassie, who now heads a department of anthropology at the Cleveland Museum of Natural History, discovered the first piece of such a skull the following excavation season. However, it had not much in common with the so much hoped for "anthropologist’s dream.
Berhane Asfaw turns out onto the flat plain to show me the site where the skull was found. Cairns testify to the seven weeks of hard work required to recover the bones. But eventually they had the skull together: The size of the incisors and some other features were reminiscent of the genus Homo. But the molars were huge. And the brain skull held at most 450 cubic centimeters, no more than that of a typical Australopithecus. These were not the remains of a living creature that looked like the Homo erectus dominated its environment. They belonged to a cunning, bipedal primate that had to hold its own among larger, faster predators, always striving to escape their jaws long enough to pass on its growing intelligence to the next generation.
The researchers called it Australopithecus garhi. Garhi means "surprise" in the Afar language. The time and place are right to be considered the ancestor of the genus Homo to come into question. But was it really him? "You will soon get an answer to that," Asfaw says on the way back to camp. "And you will get them here at the Awash."
Aramis: Great explorer’s luck
The following morning I find Asfaw, White, Wolde-Gabriel and Elema gathered around some maps. Our way will lead us through the territory of a hostile Afar clan, the Alisera. To avoid difficulties, let’s first pay a diplomatic visit to their village of Adgantole, taking with us the six Afar policemen. Moreover, Elema, as district official and head of the Bouri-Modaitu, enjoys the respect of all Afar clans on the Middle Awash. After what we hope will be a friendly meeting, the research team is to head toward Bouri-Modaitu and drop off a few of us out of sight. From there we want to continue our excursion into the past.
Adgantole is a musty-smelling, dusty village on the edge of the Awash flood plain. The Afar traditionally greet each other with the dagu, a hail of hand kisses and the exchange of news. But only a few inhabitants appear here. The chief of the clan is apparently ill and stays in his hut. Elema goes in alone to talk to him. After that we set off again. Strictly speaking, on our walk through time we would now have to stop first at a 3.4 million-year-old site called Maka. There one has the piece of a pine tree and other remains of a Australopithecus afarensis Found. But Maka is on the other side of the river. Since a bloody war between the Afar and the Issa, this terrain has been dangerous no-man’s land – good for wildlife, bad for fossil hunters.
The best known Australopithecus afarensis is "Lucy". Donald Johanson found her skeleton not far from here in Hadar in 1974. "Lucy" is about 3.2 million years old. It had a protruding snout, and its brain was not much larger than that of a chimpanzee. But her pelvis and leg bones showed that she belonged to a species that already walked upright. Her long, curved fingers and long forearms, on the other hand, suggested that she was also capable of shimmying around in the trees like a chimpanzee. Most scientists therefore insinuated that "Lucy’s" ancestors would have resembled chimpanzees even more closely. You only need the bones to prove it. But the fossils they found then caused a surprise.
"After all, we believed "Lucy" was primitive," White says as we approach the site of Aramis in our cars. "We had no idea what was really primitive."He gives the order to stop over the radio. From here we continue our way back through time on foot. We keep heading southwest, crossing a bleak landscape known as the Central Awash Com- plex (CAC). In the middle of this region lies Aramis, "Ardis" home.
Giday Wolde-Gabriel explains to me the complicated geology of the CAC. About 5.2 million years ago a lava flow poured over a huge flood plain here. On the solidified basalt many layers of sediments were deposited in the course of time. Now and then volcanic eruptions left behind thin layers of ash. Comparable to the layers of cream between the layers of a huge cake. Magma rising from the Earth’s interior pushed under one side of this pie and caused it to tilt westward. As a result, some of the lower layers have been exposed again. Our way leads us between such tilted deposits: We move horizontally through space, but in doing so we advance vertically into time.
Finally we descend a slope. Wolde-Gabriel suddenly stops and taps with his geologist’s hammer on a strip of volcanic rock, the so-called Lubaka Tuff. While that one doesn’t itself contain minerals for reliable age determination, the material directly beneath it does. It is magnetic rock. Earth’s magnetic poles have swapped south and north poles on and off over the eons, and this is evident in the orientation of magnetic minerals. Such a polarity reversal took place 4.18 million years ago, and this event has left a visible mark in the sediments of the CAC for skilled geologists.
Immediately below the layer with this "calendar entry" lies our first target: a plain covered with scattered bushes, where a fossil jawbone was found in 1994. He was a good match for fossils discovered some time earlier in Kenya by Meave Leakey and her team and named Australopithecus anamensis had baptized. Similar bones were found on the Middle Awash at a site called Asa Issie, about ten kilometers from our present location. All these fossils are a little older and more primitive than those of Australopithecus afarensis, but judging by the tibia from Kenya and a femur from Asa Issie, also the Australopithecus anamensis up-right. Possibly afarensis and anamensis only differently old representatives of one and the same species, two buds of a single evolutionary lineage on the human family tree. There is no clear boundary between them.
If we go back even further in time, then below the layer of the Australopithecus anamensis a gap in the evidence about hominid evolution at the Middle Awash. The clay we are walking over now was deposited 4.4 to 4.3 million years ago. At that time there was a lake here, and except for the remains of fish, nothing remains of it. But in the layer below lay the most beautiful find of all.
The sun-scorched lowland, through which we are now trudging, does not seem to contain any special features. With the exception of a semicircle of basaltic rocks. He identifies the site where Gen Suwa, a paleoanthropologist at the University of Tokyo, found the 17. December 1992, he saw a mysterious molar protruding from the ground. It was just recognizable as a human tooth. Days later, fossil collector Alemayehu Asfaw found the piece of a child’s mandible nearby. In it was the foremost molar of a milk dentition.
"This molar was unlike any infant tooth of early man I had ever seen, and I have seen them all," White explained to me. "Gen Suwa and I were just looking at each other. We did not have to say anything. This tooth was by far more primitive than that of a Australopithecus."