The Dawn of Human Culture (11 page)
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4
THE FIRST TRUE HUMANS
We have suggested that human evolution was characterized by a series of short, abrupt steps or punctuations, separated by long periods with little or no change. So far, we have described a possible first punctuation, which occurred between 7 and 5 million years ago and produced bipedal apes, and a better-evidenced second event, which occurred between 3 million and 2 million years ago and produced the first stone tool makers. The abruptness of each step is debatable, but the stability that followed is patent. Thus, the anatomy of the bipedal apes changed little over intervals that lasted a million years or more. The anatomy of the earliest tool makers is poorly known, but they were probably equally conservative, judging by a remarkable lack of change in the tools they produced. They may have had larger brains than the bipedal apes, but they may also have retained an ape-like upper body form and a high degree of size difference between the sexes. If so, it’s probable that they continued to rely heavily on trees 04 True Humans.r.qxd 1/29/02 5:04 PM Page 92
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for food and refuge and that they had an ape-like social organization that involved little or no cooperation between the sexes. When we know them better, we may decide that for all effects and purposes, they were “technological apes.”
We turn now to a third step that occurred about 1.8 to 1.7 million years ago. It is more fully documented than its forerunners, and it was at least as momentous, for it produced a species that anticipated living people in anatomy, behavior, and ecology, save mainly for its smaller brain. With this caveat in mind, its members can reasonably be labeled the first “true humans,” and this is how we will refer to them here. Early on, the first true humans authored a major advance in stone flaking technology, but thereafter, both their anatomy and their artifacts appear to have remained remarkably stable for a million years or more. In this respect, they were marching to the same drummer as their predecessors.
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He picked a difficult, unpromising spot, a slight rise protected by an acacia tree within a sun-baked gully. The surface was littered with 04 True Humans.r.qxd 1/29/02 5:04 PM Page 93
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black lava pebbles, and any fossils that had eroded out were likely to have been trampled by local herds of goats and camels. Kimeu’s chances seemed slim, but he had overcome such odds before, and he did so again now. He soon spotted a match-book-sized piece of black bone, hardly distinguishable from the surrounding pebbles, and when he picked it up, he knew that it came from the forehead of an extinct kind of human.
Kimeu’s assessment drew the Leakeys and their paleoanthropological colleague, Alan Walker, to the find spot, and over the next four years, they led parties that meticulously excavated the deposits nearby.
In the end, they not only managed to piece together a complete skull, they also recovered most of the skeleton that went with it. The skeleton turned out to represent an adolescent male, whom his discoverers affectionately dubbed the “Turkana Boy.” Analysis of the enclosing sediments showed that the boy had died and been rapidly buried on the edge of a marsh about 1.5 million years ago. His skeleton was even more complete than Lucy’s, found a decade earlier in deposits that were 1.8 million years older, and it is still the most complete skeleton from any human who lived before 120,000 years ago. Its significance matches that of Lucy, for if she left no doubt that her kind were bipedal apes, the Turkana Boy showed just as clearly that his kind were true humans.
Recall that Lucy was tiny—probably only about one meter (3'
3") tall, and she had very long arms relative to her legs. She also had an ape-like cone- or funnel-shaped trunk, which narrowed upwards from her pelvis to her shoulders (Figure 4.1). From a distance, a modern observer might have mistaken her for a kind of chimpanzee. The Turkana Boy was tall—about 1.62 meters (5'4") at time of death and 04 True Humans.r.qxd 1/29/02 5:04 PM Page 94
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0
0
50 cm
2 ft
“Turkana Boy”
“Lucy”
“Lucy”
(Homo ergaster)
(Australopithecus
(Australopithecus afarensis)
afarensis)
scaled to the stature of the
“Turkana Boy”
FIGURE 4.1
Stature and body proportions in the “Turkana Boy” and in “Lucy” (redrawn after C. B. Ruff 1993,
Evolutionary Anthropology
2, p. 55).
destined to reach 1.82 meters (6') or more if he had survived to adulthood. His arms were no longer, relative to his legs, than in living people, and he had a barrel-shaped chest over narrowed hips. From a distance our time-traveler might have confused him for one of the lanky Turkana herders who live around Nariokotome today.
Close up, our observer would soon realize his error, for the Turkana Boy had a skull and face that would startle any living human (Figure 4.2). His brain was nearly full grown, but its volume was a mere 04 True Humans.r.qxd 1/29/02 5:04 PM Page 95
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880 cubic centimeters (cc), only 130 cc greater than the maximum in
Homo habilis
(including all of its possible constituents) and 450 to 500 cc below the average in living people. The size increase from
habilis
all but melts away when the Turkana Boy’s larger body size is considered. His braincase—the part of the skull that enclosed his brain—
was long and low, and the skull walls were exceptionally thick. It was the thickness of the forehead fragment that first alerted Kimeu to the kind of human he had found. The boy’s forehead was flat and receding, and it descended to merge at an angle with a bony visor or browridge over his eyes. His nose was typically human in its forward projection and downwardly oriented nostrils, and in this he differed from the australopiths and
habilis
who had ape-like noses that were flush against the face. The nose aside, however, his face was striking for its great length from top to bottom, and his jaws projected far to flat, receding
long, low
forehead
braincase
browridge
face and
jaws
projecting
strongly
forwards
0
5 cm
no chin
“Turkana Boy”
0
2 in
FIGURE 4.2
The skull of the “Turkana Boy” (drawn by Kathryn Cruz-Uribe from photographs and casts) (Copyright Kathryn Cruz-Uribe).
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the front. His lower and upper jaws were massive, and they contained chewing teeth that were significantly larger than our own, even if they were smaller than the average in
habilis
or the australopiths. The bone below his lower front teeth slanted sharply backwards, meaning that he was completely chinless.
On reflection, contemplating a seemingly improbable combination of modern body and primitive head, our hypothetical observer might wonder if his companion was a visitor from an alternative universe or perhaps the product of some strange genetic experiment. In a sense, he was both, but the alternative universe was our own world long ago, and the experimenter was nature.
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Homo erectus
. The antiquity of the Asian specimens is disputed for reasons we discuss below, but most if not all are probably younger than a million years. If then, as many authorities believe, the Koobi Fora, Nariokotome, and east Asian specimens should be placed in the same species,
erectus
would have an African origin.
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The similarities between the east African and Asian fossils are unquestionable, but some specialists have also pointed to subtle and potentially significant differences. Thus, on average, the African skulls tend to be somewhat higher-domed and thinner-walled than their east Asian counterparts, and they have less massive faces and browridges.
In these respects and others, they are more primitive or less specialized, and they may tentatively be assigned to a separate species for which the name
Homo ergaster
has been proposed. The name translates roughly as “working man,” and it was first applied to some of the Koobi Fora fossils that came from deposits that also contained flaked stone tools.
The removal of the east African fossils from
erectus
to
ergaster
would be trivial if we accepted the once common notion that
erectus
was directly ancestral to
Homo sapiens,
for
ergaster
would then be simply an early stage of
erectus
. Fossils that date from after 500,000
years ago, however, now indicate that
sapiens
evolved in Africa while
erectus
continued on largely unchanged in eastern Asia (Figure 4.3).
In form and geologic age,
ergaster
is well positioned to be the ancestor not only of
erectus
but also of
sapiens,
and this is the view we adopt here.
The ancestry of
ergaster
is murky, but it may have originated suddenly from
habilis
(or from one of the variants into which
habilis
may eventually be split) in adaptive response to a sharp increase in aridity and rainfall seasonality that occurred across eastern Africa about 1.7 million years ago. Alternatively, at the end of the last chapter, we noted that future research may reveal a bush of human species between 3 million and 2 million years ago, in which case
ergaster
could represent a branch totally separate from the variants of
habilis
.
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millions of
millions of
years ago
years ago
0
0
H. neanderthalensis
H. sapiens
H. erectus H. erectus
(China)
(SE Asia)
0.5
0.5
H. heidelbergensis
1.0
1.0
1.5
H. ergaster
1.5
H. habilis
H. rudolfensis
2.0
2.0
FIGURE 4.3
A tree diagram showing the suggested relationships between
Homo ergaster
and later human species.
At Olduvai Gorge,
habilis
or one of its variants may have persisted until 1.6 million years ago, but thereafter
ergaster
survived alone. Its history after 1 million years ago is debatable, because few relevant fossils are known, but on present evidence it may have persisted largely unchanged until about 600,000 years ago, when brain size increased rapidly and new, more advanced human species arose.
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fact paleoanthropologists know that their first priority must be to understand how ancient people looked and behaved. Alan Walker and Richard Leakey, who co-directed the excavation of the Turkana Boy’s skeleton with Meave Leakey, realized that it provided a unique opportunity to explore the biology of a primitive human species. They thus invited anatomist colleagues to study it with them, and the result was a comprehensive, stimulating monographic description that fleshes out our knowledge of
ergaster
.
On average, brain volume in
ergaster
was only about 900 cc, large enough to invent the new kinds of stone tools with which it is associated, but also small enough to explain why the tools then changed little over the next million years or so. Based mainly on dental development, the Turkana Boy was probably about 11 years old at time of death, but his stature compared more closely with that of a modern 15-year-old and his brain with that of a modern 1-year-old.
