The sum has led Walker to conclude that “While he may have been smart by ape standards, relative to [living] humans the Turkana Boy was tall, strong, and stupid.” The same statement might apply equally well to everyone who lived between 1.8 million and 600,000 to 500,000 years ago, before a spurt in brain volume brought it much closer to the modern average.
Body form and size tell a different story, and in this regard
ergaster
was as human as anyone alive today. The shortening of its arms relative to its legs signals the final abandonment of any ape-like reliance on trees for feeding or refuge. A greater commitment to life on the ground meant an even greater emphasis on bipedalism, and this could explain the narrowing of the hips (pelvis) and the concomitant development of a barrel-like chest. The narrowed pelvis increased the 04 True Humans.r.qxd 1/29/02 5:04 PM Page 100
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efficiency of muscles that operate the legs during bipedal movement, and it would have forced the lower part of the rib cage to narrow cor-respondingly. To maintain chest volume and lung function, the upper part of the rib cage would have had to expand, and the modern barrel shape would follow. The narrowing of the pelvis also constricted the birth canal, and this must have forced a reduction in the proportion of brain growth that occurred before birth. Infant dependency must then have been prolonged, foreshadowing the uniquely long dependency period that marks living humans.
Pelvic narrowing must also have reduced the volume of the digestive tract, but this could have occurred only if food quality improved simultaneously. Direct archeological evidence for new foods is lacking or ambiguous, but the choices are larger quantities of meat and marrow, greater numbers of nutritious tubers, bulbs, and other underground storage organs, or both. Cooking might also be implied, since it would render both meat and tubers much more digestible, but so far, persuasive fireplaces or hearths are unknown before 250,000 years ago, by which time
ergaster
had been replaced by more advanced species.
Archeology shows that
ergaster
was the first human species to colonize hot, truly arid, highly seasonal environments in Africa, and this may partly explain why the Turkana Boy was built like a modern equatorial east African, with a lanky body and long limbs. As the trunk thins, body volume decreases more rapidly than skin area, and greater skin area promotes heat dissipation. Long limbs provide the same benefit. In people like the Inuit or Eskimo who must conserve heat, we see the reverse—stocky bodies and short limbs that reduce heat loss.
Adaptation to hot, dry conditions can also explain why
ergaster
was the first human species to have a forwardly projecting, external nose.
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In living humans, the external nose is usually cooler than the central body, and it thus tends to condense moisture that would otherwise be exhaled during periods of heightened activity. Finally, given that
ergaster
was shaped for a hot, dry climate, we can speculate that it was also the first human species to possess a nearly hairless, naked skin. If it had an ape-like covering of body hair it could not have sweated efficiently, and sweating is the primary means by which humans prevent their bodies—and their brains—from overheating.
When the Turkana Boy’s skeleton is considered with isolated limb bones from other individuals, it becomes clear that
ergaster
was not only taller and heavier than earlier humans, but also that the sexes differed no more in size than they do in living people. This stands in sharp contrast to the australopiths and perhaps
habilis,
in which males were much larger than females. In ape species that exhibit a similar degree of sexual size difference, males compete intensely for sexually receptive females and male-female relationships tend to be transitory and non-cooperative. The reduced size difference in
ergaster
may signal the onset of a more typically human pattern in which male-male competition was reduced and male-female relationships were more lasting and mutually supportive.
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seasonal environments to which it was physiologically adapted and also how it became the first human species to expand out of Africa.
The first tool makers, the Oldowan people, mastered the mechanics of stone flaking, and they were very good at producing sharp-edged flakes that could slice through hides or strip flesh from bone. At the same time, they made little or no effort to shape the core forms from which they struck flakes, and to the extent that they used core forms, it was perhaps mainly to crack bones for marrow. For this purpose, core shape didn’t matter very much.
Ergaster,
however, initi-ated a tradition in which core forms were often deliberately, even meticulously, shaped, and shape obviously mattered a lot.
The characteristic artifact of the new tradition was the hand axe or biface—a flat cobble or large flake that was more or less completely flaked over both surfaces (hence the term biface) to produce a sharp edge around the entire periphery (Figure 4.4). Many hand axes resemble large teardrops, as they narrow from a broad base or butt at one end to a rounded point at the other. Ovals, triangles, and other forms are also common, and in some places, hand axe makers produced pieces with a straight, sharp, guillotine-like edge opposite the blunt butt (Figure 4.5).
Archeologists often call such pieces cleavers to distinguish them from hand axes, on which one end tends to be more pointed.
John Frere, the great-great-grandfather of Mary Leakey, is sometimes credited as the first person to recognize the human origin and great antiquity of hand axes. In 1797, he sent a letter to the Society of Antiquaries in London describing two carefully crafted hand axes he had recovered from ancient lake deposits at Hoxne in Suffolk, England.
Bones of extinct animals occurred nearby, and Frere concluded that the hand axes had been “used by a people who had not the use of metals”
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0
0
5 cm
2 in
Early Acheulean
(Sterkfontein Member 5)
Late Acheulean
(Kathu Pan)
FIGURE 4.4
An early Acheulean hand axe from Sterkfontein Cave and a late Acheulean hand axe from Kathu Pan (top redrawn after K. Kuman 1994,
Journal of Human Evolution
27, fig. 6; bottom drawn by Kathryn Cruz-Uribe from the original).
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Early Acheulean
(Sterkfontein Member 5)
0
0
5 cm
2 in
Late Acheulean
(Elandsfontein Cutting 10)
FIGURE 4.5
An early Acheulean cleaver from Sterkfontein Cave and a late Acheulean cleaver from Elandsfontein Cutting 10 (top redrawn after K. Kuman 1994,
Journal of Human
Evolution
27, fig. 6; bottom drawn by T. P. Volman from the original).
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and belonged “to a very ancient period indeed, even beyond the present world.” Frere’s archeological colleagues largely ignored his opinion, and it was the French customs official Boucher de Perthes who first forced the issue. Between about 1836 and 1846, de Perthes collected hand axes and bones of extinct mammals from ancient gravels of the Somme River near the town of Abbeville in northern France. He concluded that “In spite of their imperfection, these rude stones prove the [ancient] existence of man as surely as a whole Louvre would have done.” His claims were initially spurned, but they gained credibility in 1854 when Dr. Rigollot, a distinguished and previously vocal skeptic, began finding similar flint axes in gravels near St. Acheul, a suburb of Amiens. In 1858, the eminent British geologist Joseph Prestwich visited Abbeville and St. Acheul to check the claims for himself. He came away convinced, and the case was made. Archeologists subsequently assigned ancient tool assemblages with hand axes to the Acheulean Culture or Industry, named for the prolific locality at St. Acheul. Later, when similar artifacts were recognized in Africa, they were also assigned to the Acheulean, and we now know that the Acheulean was present in Africa long before it reached Europe.
The oldest known Acheulean tools are dated to 1.65 million years ago, and they come from the same west Turkana region of northern Kenya that provided the Turkana Boy, though not from the same site.
Acheulean artifacts are also well documented at 1.5 to 1.4 million years ago at Konso in southern Ethiopia, on the Karari Escarpment east of Lake Turkana in northern Kenya, and at Peninj near Olduvai Gorge in northern Tanzania. In each case, potassium/argon dating has verified their antiquity just as securely as it demonstrates the presence of
ergaster
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oldest
ergaster
and the oldest Acheulean is probably not coincidental.
Peninj has provided a lower jaw of the robust australopith,
Paranthropus
boisei
, but this shows only that
boisei
persisted after
ergaster
emerged
,
not that
boisei
made Acheulean tools. Konso has provided an upper third molar and the left half of a lower jaw with four teeth from
ergaster,
and
ergaster
is the more likely tool maker. This is not only because it had a larger brain than
boisei,
but because Acheulean tools continue on largely unchanged after one million years ago, when
boisei
had become extinct.
The Acheulean surely originated from the Oldowan, and the oldest Acheulean assemblages often contain numerous Oldowan-style core forms and flakes alongside Acheulean hand axes. In a broad sense, the Oldowan core forms anticipate Acheulean bifaces, but no Oldowan or Acheulean assemblage contains tools that are truly intermediate between the two, and the biface concept seems to have appeared very suddenly in a kind of punctuational event like the one that may have produced
ergaster
. The earliest biface makers made one other note-worthy discovery that was often tied to biface manufacture—they learned how to strike large flakes, sometimes a foot or more in length, from large boulders, and it was from these that they often made hand axes and cleavers. Ancient stone tool assemblages that contain large flakes can be assigned to the Acheulean even on those occasions when, perhaps by chance, the assemblages lack hand axes.
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ened at sites like Melka Kunturé in Ethiopia, Olorgesailie in Kenya, Isimila in Tanzania, and Kalambo Falls in Zambia, where hand axes occur by the hundreds, often crowded close together and with no obvious signs of use. Such sites have prompted archeologists Marek Kohn and Steven Mithen to propose that the hand axe may have been the Acheulean equivalent of a male peacock’s plumage—an impressive emblem for attracting mates. When a female saw a large, well-made biface in the hands of its maker, she might have concluded that he possessed just the determination, coordination, and strength needed to father successful offspring. Having obtained a mate, a male might simply discard the badge of his success, alongside others that had already served their purpose.
The mate selection hypothesis cannot be falsified, but sites with large concentrations of seemingly unused hand axes are less common than ones where hand axes are rarer and sometimes do show signs of use. Since the tools come in a wide variety of sizes and shapes, the probability is that they served multiple utilitarian functions. Some of the more carefully shaped, symmetric examples may have been hurled at game like a discus; other more casually made pieces may have served simply as portable sources of sharp-edged flakes; and yet others could have been used to chop or scrape wood. Experiments have also shown that hand axes make effective butchering tools, particularly for dismembering the carcasses of elephants or other large animals.
The truth is that hand axes may have been used for every imaginable purpose, and the type probably had more in common with a Swiss Army knife than with a peacock’s tail.
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inception at roughly 1.65 million years ago until its end at about 250,000 years ago. Harvard archeologist Glynn Isaac, who analyzed the Acheulean artifacts from a deeply stratified sequence at Olorgesailie, Kenya, remarked that the Acheulean displays a “variable sameness”
and strikes “even enthusiasts as monotonous.” By “variable sameness”
he meant that changes in hand axe form from layer to layer or time to time seem to have been largely random and there is no obvious direc-tional trend. Often, where hand axes in one assemblage appear more refined than they do in another, the reason may be that the people had different raw materials at their disposal. Flint or chert, for example, is usually much easier to flake than lava, and where people could get large enough pieces of flint, their hand axes will tend to appear more finely made for this reason alone.