The Dawn of Human Culture (9 page)
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up to Oldowan standards. The cores have a battered look, reflecting Kanzi’s many unsuccessful attempts to strike flakes, and his flakes are mostly tiny and difficult to distinguish from naturally fractured pieces.
In sum, despite having the best possible human mentor, Kanzi has never mastered the mechanics of stone flaking, and if his products turned up in an ancient site, archeologists would probably not accept them as unequivocal artifacts. Kanzi’s younger sister, Panbanshiba, has now also been encouraged to flake stone, and there are plans to involve common chimpanzees. Archeologists await the results with interest, but the evidence so far suggests that even an especially intelligent and responsive ape cannot grasp the mechanics of stone flaking.
* * *
So far, no cluster has provided unequivocal traces of fireplaces or of structures that would imply anything more.
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Cut and bash marks show that Oldowan people handled the bones at their sites, but carnivore-damaged specimens are also common, and this raises the question of how the people obtained the bones.
Some archeologists argue for hunting or for confrontational scavenging in which groups of people drove carnivores off still-fleshy carcasses. Others argue for more passive scavenging from carcasses that carnivores had largely consumed. In advance, the simplicity of Oldowan technology may favor passive scavenging, but direct evidence is sparse, and naturalistic and experimental observations can be used to support hunting or scavenging. We know, for example, that carnivores largely ignore limb bone shafts that people have smashed, because the marrow is gone and the shaft fragments themselves have little food value. In Oldowan sites, limb bone midshaft fragments from antelopes and other animals often show numerous carnivore tooth marks, and this may mean that the people mainly scavenged from carcasses on which carnivores had already fed. Yet, we also know that carnivore feeding tends to remove the most nutritious skeletal elements first. These are bones of the upper fore limb (humeruses and radioul-nas) and upper rear limb (femurs and tibias) that are especially rich in meat, marrow, and grease. Compared to less desirable parts, such bones tend to be common in Oldowan sites, and this might mean that the people often got to carcasses first and did not have to settle for scraps—
in short, that they were hunters or confrontational scavengers.
Passive scavenging could still have been the rule, however, if we assume that Oldowan people favored environments with few hyenas, so that they could scavenge directly from lions or other large cats.
Lions deflesh limb bones but often leave the shafts intact, and in the absence of hyenas, scavenging people might still have been able to 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 76
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obtain numerous marrow-rich, meatless arm and leg bones. Marrow alone, however, provides relatively little food value, particularly when the effort to remove it is considered, and scavenging focused on marrow would provide little sustenance, unless lion kills were far more abundant than they are in most historic African environments. In addition, the most nutritious limb bones at Oldowan sites often show cut marks from flesh removal, which suggests that the people got the bones before someone else picked them bare.
The bottom line is that the available evidence can be read to favor either hunting or passive scavenging, and the surviving data may never allow a firm choice. Still, the uncertainty over hunting vs. scavenging should not be allowed to obscure a far more fundamental point.
About 2.5 million years ago, bipedal creatures that were probably no more technological or carnivorous than living chimpanzees evolved into ones who mastered the physics of stone flaking and then used their newfound knowledge to add an unprecedented amount of meat and marrow to their traditional vegetarian diet.
* * *
million years ago, and the recent discovery of
Kenyanthropus platyops
can only fuel the debate. Before
platyops
was found, most authorities agreed that
Australopithecus afarensis
was the only human species 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 77
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between 3.5 and 3 million years ago and that it was ancestral to all later people. It may still be the most plausible ancestor for some or all, but
platyops
provides an alternative that cannot be ruled out a priori.
Equally important, it suggests that fresh finds may only expand the choices, if like
platyops
they reveal yet additional, unexpected australopith species. What remains clear is that when Oldowan tools appeared around 2.5 million years ago, people were divided between at least two distinct evolutionary lines. One led to the later robust australopiths and the other to the genus
Homo
(Figure 3.5).
We do not know when the two lines separated, but a reasonable working hypothesis is that they diverged abruptly between 2.8
and 2.5 million years ago, when a climatic inflection reduced moisture across much of Africa and sparked extinctions and new species in antelopes and other mammalian groups. The key point here is that the lines were already separate when Oldowan tools appeared, and we must therefore contemplate more than one potential tool maker. No one doubts that early representatives of
Homo
produced stone tools, but what about the robust australopiths? The question is not hypothetical, since flaked stones have been found with
robustus
at Swartkrans Cave in South Africa and with its east African cousin,
boisei,
at Olduvai Gorge and other sites in eastern Africa.
Anthropologist Randall Susman of the State University of New York at Stony Brook has proposed a rule of thumb for determining whether robust australopiths produced Oldowan artifacts. He notes that chimpanzees have curved, narrow-tipped fingers and short thumbs.
This hand structure promotes a power grip that is helpful for grasping tree limbs. Humans, in contrast, have shorter, straighter fingers with broad tips and larger, stouter thumbs. The human hand promotes a 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 78
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Homo
Homo
Homo
Artifact Traditions
millions of
neanderthalensis
sapiens
erectus
millions of
Later Stone Age &
years ago
years ago
Upper Paleolithic
0
0 0.05
0.25
Middle Stone Age
Paranthropus
& Mousterian
Homo
boisei
heidelbergensis
1
1
Acheulean
Homo
(or
Kenyanthropus
)
rudolfensis
Homo
Paranthropus
1.65
Homo
habilis
robustus
2
ergaster
2
Oldowan
?
Australopithecus
2.5
garhi
?
?
Paranthropus
3
aethiopicus
3
Australopithecus
?
africanus
Australopithecus
afarensis
Kenyanthropus
platyops
(flaked stone
4
Australopithecus
4
artifacts
?
anamensis
unknown)
?
?
Ardipithecus
5
ramidus
5
?
Orrorin
tugenensis
6
6
FIGURE 3.5
A tree diagram (phylogeny) linking human species. Dotted bars indicate tentative time ranges.
The broad outline of the tree is established, but new discoveries may alter the proposed connections between the branches.
precision grip that is well suited for opening a jar, writing with a pencil, or flaking stone. The chimpanzee/human difference is manifest in the first or thumb metacarpal, the bone at the edge of the palm that runs between the wrist and the thumb itself. In chimpanzees, the thumb metacarpal is relatively short, and it is narrow, particularly at the end where it articulates with the first bone (phalange) of the thumb (Figure 3.6). In humans, it is relatively longer and broader, and in combination 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 79
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damaged
after death
broad
narrow
tip
tip
broad
narrow
shaft
shaft
modern
Paranthropus
Australopithecus
modern
human
robustus
afarensis
chimpanzee
(Swartkrans)
(Hadar)
0
5 cm
0
2 in
FIGURE 3.6
Thumb metacarpals of a modern human,
Paranthropus robustus, Australopithecus afarensis
, and a chimpanzee (redrawn after R. L. Susman 1994, Science 265, fig. 3).
with a broader thumb tip, it provides attachment for three muscles that chimpanzees lack and that promote precision grasping in humans.
No tools are associated with
Australopithecus afarensis,
and Susman’s criterion suggests that none were to be expected, since
afarensis
had a chimpanzee-like thumb metacarpal. Tools abound with much later
Homo erectus
and
Homo neanderthalensis,
and again in keeping with advance expectations, both had typically human thumb metacarpals. Tools also occur at robust australopith sites, but in this instance, no prediction is possible because the same sites usually 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 80
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contain bones of early
Homo
. And therein lies a dilemma. Early
Homo
and robust australopiths can be cleanly separated only on their teeth and skulls. The isolated limb bones that occur at most sites could come from either. At Swartkrans, these bones include a thumb metacarpal that Susman assigns to
robustus,
because unequivocal
robustus
teeth and skull parts heavily outnumber those of
Homo
. In form, the metacarpal is typically human, and if Susman’s assignment is accepted, it could imply that
robustus
made some or all of the Swartkrans stone tools. The problem is that the metacarpal could represent
Homo,
and this might even seem likely, since it strongly resembles thumb metacarpals in much later humans. In short, thumb metacarpal form does not unequivocally finger
robustus
as a stone tool maker.
It remains possible, of course, that both
robustus
and early
Homo
made stone tools, but if so, we might expect two distinct tool traditions between 2.5 million years ago and the time when
robustus
and its east African relative,
boisei,
became extinct, at or shortly before 1
million years ago. Oldowan tools may be too crude to reveal separate traditions, but tools of the Acheulean Industry or Culture that replaced the Oldowan 1.7 to 1.6 million years ago were more formal, and they suggest only one evolving tradition. No one questions that
Homo
alone produced the Acheulean tradition, since it persisted long after the robust australopithecines had disappeared.
This is not to say that
robustus
made no tools, and it could be responsible for some polished bone fragments found at Swartkrans and at nearby Drimolen Cave. Experiments with modern replicas indicate that the polish formed when someone used the fragments to open termite nests. Chimpanzees savor termites, and in some groups, individuals routinely probe nests with modified branches. If
robustus
had 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 81
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developed a more aggressive twist on this basic strategy, its success could explain a peculiarity in the carbon composition of its dental enamel. Carbon comes in two naturally occurring non-radioactive forms (isotopes)—carbon 12 (12C) and carbon 13 (13C)—and in tropical or subtropical environments like those that
robustus
inhabited, grasses tend to be significantly richer in 13C than leaves, tubers, fruits, or nuts.
The ratio of 13C to 12C in the tooth enamel of an animal reflects the ratio in its preferred foods, and a team of geochemists led by Julia Lee-Thorp of the University of Cape Town has shown that
robustus
enamel is relatively enriched in 13C.
Robustus
individuals must thus have been feeding fairly heavily on grasses or on grass-eating animals. Grass-eating itself can be ruled out, because grasses contain small, hard particles (phytoliths) that score teeth in a distinctive way, and
robustus
teeth lack the signature scratches. Feeding on grass-eating antelopes or other mammals cannot be dismissed, but focusing on grass-eating termites or other invertebrates would have been far less risky.