Out of africa

WHERE WAS THE CRADLE OF HUMANKIND?

The Neanderthals, whose remains provided the first evidence for the existence of fossil humans, have continued to play a major role in evolution research. In order to understand the appearance and disappearance of the Neanderthals, it is necessary to take a look at the early history of our forebears, and the tale of their discovery.

Far from what were then regarded as the "cradles of humanity"—south-east Asia and Europe—a discovery was made in Taung, South Africa, in 1924 that excited the still young field of paleoanthropology to a degree second only to that caused by the Neanderthal and the Pithecanthropus erectus from Java. Quarriers uncovered a fossil child's skull, which the Johannesburg anatomy professor Raymond Dart soon afterward presented to the skeptical profession under the name Australopithecus africanus (African southern ape). The fossil, about a million years old, immediately became the oldest known pre-human find. The small but fine discovery was especially fascinating because of the position of the foramen magnum, the place where the spinal cord enters the brain. This opening was on the underside of the skull and not, as in anthropoid apes, at an angle behind. To be sure, the brain was hardly bigger than that of a chimpanzee, but several sections displayed a distinctly different structure. The canine teeth were much smaller than those of anthropoid apes. These characteristics directly contradicted the dominant theories of the time, because most scientists thought that the purported "missing link" had already been found with the Piltdown Man. The Taung Child, as Dart, almost lovingly, named it, was not the only fossil from Africa. Already in its discovery year, 1921, the skull of the 300,000-year-old Rhodesian Man, from what is now Kabwe in Zambia, was placed in the line of relationship with Heidelberg Man and the Neanderthal. Although interesting for the still sparsely populated human family tree, this find was too recent to be of much help in tracking the origin of our species. For a long time, the scholarly world scorned the more important find, the Taung Child. The "tale of misfortunes" appeared to repeat itself, because just like the Neanderthal and Java Man it shared the fate of being a "misunderstood fossil" after its discovery. In retrospect, the ground for the stepmotherly treatment of Dart's African southern ape was simple: hardly a single scholar was willing to accept the possibility of human forebears in Africa. They would have been more prepared to accept such a fossil, if at all, from Asia.

About fifty kilometers southwest of Beijing the "Chinese man from Peking"—Sinanthropus pekinensis—was discovered between 1927 and 1937. The skull fragments, bones, jawbone, and tooth finds, between 200,000 and 500,000 years old, displayed marked similarities to Java Man, including strongly pronounced eyebrow ridges, a flat, receding forehead, a jutting jaw, and massive bones. All these characteristics were also reminiscent of the find from the Neander Valley; the only significant difference was that the cranium attested to a smaller brain volume. The scholars were agreed that Peking Man was an early human, even more "primitive" and archaic in anatomy than the already-known Neanderthals. Could Peking Man have been a forerunner of European Neanderthals? The conclusion was obvious, but it was only the subsequent finds of the Dutch-German scientist Gustav Heinrich Ralph von Koenigswald that linked these Chinese discoveries (which have since vanished) with comparable pieces from Java (Figure 6). He showed that all the Asian fossil humans belonged to the species Homo erectus, the oldest offshoot then known of the genus Homo. Despite the existence of the million-year-old child from Taung in Africa, Asia was therefore reserved as the original home of humankind.

Nonetheless, one person believed in the original African heritage of humans. The paleontologist Robert Broom, a Scot by birth, world traveler, and research-loving crank, was one of the few significant scholars who supported Raymond Dart's hypothesis that the Taung find was a very old human forebear. In 1936, Broom found the skull of an adult Australopithecus in a cave near Sterkfontein, about fifty kilometers southwest of Johannesburg. With this discovery, Broom declared the existence of the new genus Plesianthropus. A decade later, he found a skull with female characteristics, calling it "Mrs. Ples." The anatomical features of pre-humans already recognized in the Taung Child were now confirmed with the adult Mrs. Ples.

At this point, starting in the 1940s, a reversal of scholarly opinion began to make itself felt. Countless additional finds gave clear evidence that the cradle of humankind must have lain in Africa. Up to the present, more

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Figure 6 (a) Sangiran 2 is the cranium of a hominid (H. erectus) from Sangiran on Java (Indonesia). It was excavated in the late 1930s by G.H.R. von Koenigswald, and represents the c. 800,000-year-old skull of the Asiatic Homo erectus. (b) D 2282 from the site Dmanisi in Georgia is one of the oldest Homo erectus finds in Europe. The fossil, c. 1.7 million years old, attests to the early emigration of primitive human beings from Africa.

Figure 6 (a) Sangiran 2 is the cranium of a hominid (H. erectus) from Sangiran on Java (Indonesia). It was excavated in the late 1930s by G.H.R. von Koenigswald, and represents the c. 800,000-year-old skull of the Asiatic Homo erectus. (b) D 2282 from the site Dmanisi in Georgia is one of the oldest Homo erectus finds in Europe. The fossil, c. 1.7 million years old, attests to the early emigration of primitive human beings from Africa.

than 500 remains of australopithecines have been found at Sterkfontein alone. Recently, Ron Clarke even discovered the skeleton of a pre-human there that is over 90 percent complete, including the skull, a find that has become famous as "Little Foot." Within sight of Sterkfontein are the Kromdraai and Swartkrans Caves. Robert Broom achieved his second great coup in Kromdraai in 1938: he provided evidence that there was a second variety of Australopithecus, significantly more robust than the specimens found at Sterkfontein. He differentiated the new find from the gracile australopithecines from Sterkfontein by labeling the robust australopithicines from Kromdraai as Paranthropus. His hypothesis, according to which the early hominids split into two lines, one vegetarian and robust, the other omnivorous and more lightly built, has been confirmed up to the present by many further discoveries. Nonetheless, there is still no general agreement in the scholarly community about whether the robust varieties constitute a different genus or only a different species.

About 280 kilometers north of Johannesburg, at a place called Makapansgat, James Kitching discovered some blackened bone fragments in a cave in 1947. He was, to be sure, not the first to happen upon such remains. Back in 1927 Raymond Dart had heard of the existence of fossil bones that he regarded, because of their blackened condition, as evidence that the hominids who had lived there used fire. Thus Dart described the australopithecenes from Makapansgat as Australopithecus prometheus, convinced that he had found the first fire user, the Prometheus of the hominids as it were. Today, however, we interpret the black color as natural manganese staining. In the 1950s and 1960s nearly twenty hominid fragments were recovered from Makapansgat, now classified as Australopithecus africanus.

Not just South Africa but Kenya and Tanzania astonished the paleontological world. Louis Leakey started his quest for the existence of human ancestors there in the early 1930s, with special interest in stone tools. He turned his attention to the Olduvai Gorge in northern Tanzania, discovered for the scholarly world in 1911 by Wilhelm Kattwinkel (the researcher of sleeping sickness), and geologically investigated by Hans Reck in 1913. There, Leakey began his painstaking archaeological and paleontological investigation. But it was Louis' wife, Mary, who finally made eastern Africa's decisive hominid find in 1959. Until that point, knowledge of the earliest phases of human evolution had come exclusively from South Africa. With the skull of the "Nutcracker Man" that Mary Leakey found, (given the scientific name Zinjanthropus boisei and classed among the robust australopithecines), an unusual series of hominid finds began that was not limited to the Olduvai Gorge. In 1964, what was at that time the oldest species in the genus Homo, Homo habilis, was discovered at the same level, the ancient humans who had possibly made and used the stone tools that were also uncovered.

Laetoli provided a further site for African finds, which Louis and Mary Leakey discovered in 1935. In the same region, in 1939 the German ethnologist Ludwig Kohl-Larsen found an upper jaw fragment with two teeth and a separate incisor. Further remains were uncovered in the 1970s, now regarded as Australopithecus afarensis. But then in 1979 Mary Leakey's team made one of the most important discoveries in the history of paleoanthropology. They had recognized numerous mammal prints in the volcanic ash layer ever since the beginning of their excavation, a process that culminated in the discovery of australopithecine footprints. This find proved that pre-humans had already fully developed the ability to walk upright about 3.6 million years ago.

The excavations of Richard Leakey, Louis and Mary's son, on the eastern bank of Lake Turkana in Kenya (Koobi Fora) have since 1972 yielded more than 120 skull fragments, teeth, and parts of skeletons, predominantly from robust australopiethecines and members of the genus Homo. The site has become the best-investigated region of hominid finds in Africa. In the 1960s the first hominid fragments were uncovered in Lothagam (6-7 million years old) and in Kanapoi (4 million years old). Maeve Leakey (Richard Leakey's wife) and her team discovered several four million-year-old jawbones in 1994 and 1995, as well as loose teeth ofhominids that were labeled Australopithecus anamensis ("anam" means "Lake" in the Turkana language). In Hadar, Ethiopia, in 1974 an American-French expedition directed by Donald Johanson and Yves Coppens dug up the skeleton of an Australopithecus afarensis, the famous "Lucy," named after the Beatles' song "Lucy in the sky with diamonds." Nearly 40 percent of the skeleton had survived, creating a small sensation.

With the discovery of Lucy and Co., at last it was clear not just to the scholarly world but to the interested public that the cradle of humanity lay in Africa, and the evolution of our original ancestors began with bipedalism, not with the development of a larger brain. Bipedalism meant that the hands no longer needed to be used for movement and were thus free for other activities. This was the precondition for the development of a tool culture, and with the addition of this it was possible to exploit a wider range of food—favorable conditions for the enlargement of the brain that started about two million years ago. Curiosity and the beginning of a "forward-looking" lifestyle could have played a role for the first time at this signpost in the history of development.

BIPEDALISM

Where, when, and how did an upright method of moving from place to place develop? A look at a prehistoric weather map can help to answer this question. The African rainforest, the habitat of our anthropoid ape forebears, originally stretched across Africa from the west coast to the east coast. Between nine and seven million years ago it shrank to its modern boundaries, thanks to global and regional climate changes. A direct consequence of this shrinkage was the creation of a broad periphery of bush and riverine landscapes all around the rim of the tropical rainforest. This was an ideal region for the emergence of bipedalism by which, according to the bank hypothesis (see below), life on the water and the search for food in it were decisive factors.

With a geographical expanse of at least four million square kilometers, it is improbable that only a single form of upright walkers emerged. One must rather assume that various geographical variants of the earliest bipedal pre-humans developed. It is unknown how precisely this change came about, because so far few finds have been made from this period. In 2000, the paleoanthropologists Brigitte Senut and Martin Pickford published fossil fragments of "Millennium Man" (Orrorin), a six million-year-old pre-human from Kenya. A year later, in 2001, Yohannes Haile-Selassie dubbed the find, discovered in Afarsenke, Ethiopia, Ardipithecus ramidus kadabba and dated it to over five million years bp. In 2003, another spectacular discovery followed, this time made by Michel Brunet's team in the desert of Chad. This find, Sahelanthropus tchadensis, or "Toumai," as the fossil was nicknamed, is thought to be seven million years old. All of the hominids represented by these finds walked upright, and all three of these new entries on the human family tree lived on the fringe of the tropical rainforest. Thus the formerly popular savannah theory (which argued that bipedalism developed to obtain a better view in the grassy savannah) was superseded as the foundation for the emergence of bipedalism. The new discoveries showed, though, that an upright posture developed long before the spread of Africa's grassy savannah. Replacing the savannah theory was the very convincing bank hypothesis, propounded by the Berlin anthropologist Carsten Niemitz. He proposed that humans developed the ability to stand on two legs in the water. Nowhere is walking on four feet as disadvantageous as in water. A logical resulting action is to raise the upper body, because the water resistance is thus decreased, the view is better, and both hands remain free to bring food safely to the bank. Upon examination of the body-mass concentrations of primates and humans, it was striking that primates, unlike other four-legged animals, carry 60-70 percent of their weight on the hind legs, so that rising to the vertical was a step that could also be accomplished anatomically, at least when in the water. Owen Lovejoy, who examined the famous Lucy's skeleton, offers another explanation. Basing his theory on the great importance of mating for humans, he speculated that childrearing could have prevented females from collecting food. They were therefore dependent on the male members of the group. Bipedalism could therefore have developed because males had to bring food to their "partners." The need for free hands to carry food thus was built on the supposed existence of a social system.

The theory of Peter Wheeler, on the contrary, is based on physiology. He argues that the heat of the tropical African savannah placed a heavy strain on those who lived there. In order to "get out of the way" of the radiating heat, in the most literal sense, the pre-human minimized the surface area exposed to the sun and began to go upright. By holding the body this way, the heat would strike only head and shoulders, while four-legged creatures receive the sun's full force on the entire back and head. One should not forget the earth's reflected heat either, which provides additional warmth to the feet and belly. This interpretation would also explain early humans' hair loss—reduced body hair along with increased sweat secretion through sweat glands could cool the entire body.

However often and in however many places the initial impetus came for the "discovery" of bipedalism will with luck be fixed by future discoveries. One point that can be made from the existing remains of the first bipedal walkers from Africa, though, is that our oldest ancestors, with or without Neanderthals in their close kin group, cannot be traced back to a single "missing link." Rather, they show that the line of descent of our forebears consists of something much more like a broad family "bush", with geographical variants, than it does a linear family tree. The spread of australopithecines across Africa from four to three million years ago attests this point very well, because the different species did not all come from a single region. We will encounter this view of geographical isolation and species formation with the later Neanderthals.

THE EARLIEST HUMANS

But what about the origin of humans? How, when, and where did our genus, Homo, emerge? So far, nearly 200 hominid fragments have been found, which should be reckoned in the broadest sense as early members ofthe genus Homo. The remains come from about forty individuals. Today scholars recognize the existence of two earliest Homo types. Homo rudolfensis lived 2.5 to 1.8 million years ago (Malawi, Kenya, Ethiopia)

and Homo habilis 2.1 to 1.8 million years ago (Kenya, Tanzania, South Africa). Confusing for scholars and laypeople alike is the blending together of australopithecine and Homo characteristics in the two. While Homo rudolfensis (the earliest evidence for which, a 2.5 million-year-old lower jaw, was uncovered by the Hominid Corridor Research Project [HCRP] in 1991 in Malawi) attests a primitive set of teeth but appears already Homo-like in its walking apparatus, Homo habilis with its reduced tooth roots shows progress in dentition, but in skeletal structure is more like pre-humans than humans. Evidently there was an alternative to the powerful chewing apparatus of the robust pre-humans, so that in certain climatic conditions, especially dryness, they could deal with harder food: tools. Very ancient pebble tools were discovered in 1995 near Gona, Ethiopia, which were about 2.6 million years old. New finds on the west bank of Lake Turkana also established that already by c. 2.5 million years bp the first tool cultures had been established—contemporaneous with the emergence of the genus Homo. But the most famous stone tools have come from the Tanzanian Olduvai Gorge. So-called pebble-choppers were purposely made here by Homo habilis and later Homo erectus. Stone materials for these tools, from what is known as the Oldowan Culture, were collected from an area of two to three kilometers and later worked. Was it the first appearance of the human as a forward-looking tool-maker, who despite the unfairness of the environment made himself independent of nature? In nature it was no new phenomenon. "Tools" in the sense of implements are widely used in the animal kingdom, especially among the primates. With humans, this increasing independence from habitat indeed led to an increasing dependence on the tools they used, still a characteristic feature of our species.

About two million years ago a new hominid variety began to develop in Africa. The "newcomer" was equipped with a powerful, large skeleton and a massive skull—the typical features of the Homo erectus, which at the time of first discovery of Java Man and Peking Man had been mistakenly labeled as the first upright walker (erectus). From our current perspective, though, it is not its bipedal stance that makes the Homo erectus significant, but rather its large brain and the ability to move quickly. The Homo erectus finds from Java and China already attested to the early humans' large brain cavity. The anatomy ofthis human type was especially confirmed by OH9 (Figure 7a), the skullcap of a c. 1.2 million-year-old find from Olduvai, and Richard Leakey's discoveries on the east bank of Lake Turkana in northern Kenya. KNM-ER 3733 (Figure 7) and KNM-ER 3883 are the catalogue numbers of the best-known remains of Homo erectus, dated to about 1.7 million years bp. These early human fragments were superseded, however, by the discovery of a nearly complete skeleton

Figure 7 (a) All together Homo erectus: the hominids KNMER 3733, OH 9, and the nearly complete skeleton of the so-called "Turkana Boy" KNM-WT 15000 show a far greater brain volume by comparison to the pre- and proto-humans that preceded them. KNMER 3733 was discovered in Koobi Fora, Kenya, by Bernard Ngeneo in 1975; with an age of 1.75 million years, it numbers among the early Homo erectus (Homo ergaster). (b) In 1960, Louis Leakey had already found the 1.4 million-year-old OH 9 in the Olduvai Gorge of Tanzania, a skullcap with massive supraorbital ridges and a brain volume of over 1000 cm3. (c) The 1.50-meter tall skeleton of "Turkana Boy" was discovered near Nariokotome, West Turkana, Kenya, in 1984. With an age of 1.6 million years, it is the most complete skeleton of an early human that has been discovered.

Figure 7 (a) All together Homo erectus: the hominids KNMER 3733, OH 9, and the nearly complete skeleton of the so-called "Turkana Boy" KNM-WT 15000 show a far greater brain volume by comparison to the pre- and proto-humans that preceded them. KNMER 3733 was discovered in Koobi Fora, Kenya, by Bernard Ngeneo in 1975; with an age of 1.75 million years, it numbers among the early Homo erectus (Homo ergaster). (b) In 1960, Louis Leakey had already found the 1.4 million-year-old OH 9 in the Olduvai Gorge of Tanzania, a skullcap with massive supraorbital ridges and a brain volume of over 1000 cm3. (c) The 1.50-meter tall skeleton of "Turkana Boy" was discovered near Nariokotome, West Turkana, Kenya, in 1984. With an age of 1.6 million years, it is the most complete skeleton of an early human that has been discovered.

at Nariokotome on the west bank of Lake Turkana (Figure 7b). The fossil bone, skull, and tooth characteristics allowed those investigating the skeleton to determine that the individual was only twelve years old at time of death. The "Nariokotome Boy" or "Turkana Boy" was notably tall for his age, a full 1.62 meters at the time of his death. He was a giant by comparison to the pre-human adult Lucy, who was only 1.30 meters tall. The height made sense, because longer legs made it possible for Homo erectus to be more active—crossing savannah, hunting, and possibly running.

The increasing body size and improved motor skills in human evolution go hand in hand with the enlargement and specialization of the brain. The slow enlargement of the thought organ from the pre-human Australopithecus brain to that of the early human Homo erectus is notable. The brain volume of a Nutcracker Man measured only 400-500 cubic centimeters, the "Able Man" (Homo habilis) between 500 and 800, and the Homo erectus between 700 and 1300 cubic centimeters. The size of the brain nearly tripled, with the consequence still seen today of a large skullcap. A reason for this "memorable" development in human evolution might, among other causes, have been fights for precedence and the emergence of social behaviors, which gave humans enough "food for thought" to develop further. A less speculative explanation can be found in prehistoric cooking. The "discovery" of fire and the invention of stone tools revolutionized our ancestors' Pleistocene menu. Meat—freshly killed or the leftovers scavenged from carnivores' meals—became part of our forebears' diet and, as a source of protein, significantly increased the potential for brain growth.

The purposeful use of fire can be seen starting about 1.5 to 1.2 million years ago. By comparing the burn traces on bones in a bush fire and in a cooking fire, the first controlled use of fire can be proven at the South African site Swartkrans. The mastery of fire certainly presented the early human Homo erectus with a challenge that led to a functioning social order. For it was desirable to transport, regularly stoke, and control fire so it could serve as protection against wild animals, provide warmth, or serve as "kitchen helper." Both the ability to use fire and early humans' ability to make tools were the preconditions for the next chapter in human history, when the human being left Africa and conquered the "Old World."

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