The Dawn of Human Culture (10 page)
* * *
Paranthropus boisei
. They found it in 1959 at site FLKI near the very bottom of the Gorge, where it was accompanied by numerous Oldowan tools and fragmentary animal bones. Understandably, they assumed that
boisei
made the tools and 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 82
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collected the bones. (They initially spoke of
Zinjanthropus boisei
or
“Boise’s east African man” in honor of one of their financial sponsors.
The species was subsequently reassigned to
Paranthropus,
but
Zinjanthropus
or “Zinj” lives on in the vernacular, and FLKI is often known alternatively as FLK-Zinj.) In 1961, the paleoanthropological world was electrified when Louis, Jack Evernden, and Garniss Curtis, two pioneers in potassium/argon dating from the University of California at Berkeley, announced that “Zinj” and his tools were 1.75
million years old. The date itself stirred a revolution, since to that point, many authorities, Louis Leakey included, assumed that human evolution might have spanned no more than a million years. Suddenly there was a lot more time to accommodate both biological and behavioral change.
The discovery of “Zinj” enabled the Leakeys to obtain funding to excavate other 1.8- to 1.6-million-year-old Olduvai sites, and they soon recovered remains of a second, larger-brained, smaller-toothed, bipedal species. Louis and his anatomist colleagues Phillip Tobias and John Napier formally described it in
Nature
in 1964, and they dubbed it
Homo habilis,
or “handy man” to signal their belief that it—and not Zinj—was the Oldowan tool maker. They and others reasoned that brain enlargement fostered tool-making and that tools to process food fostered smaller chewing teeth. In reducing “Zinj” to non-technological status, they anticipated the position we have taken here. However, the years have not been kind to
habilis,
and there is now reason to question its status as a species and as a tool maker.
In a nutshell, the difficulty for
habilis
comes down to this.
Between 1969 and 1975, a team led by the Leakeys’ son Richard recovered numerous skulls, jaws, and other bones from deposits dated between 1.9 and 1.6 million years ago at Koobi Fora on the eastern 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 83
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margin of Lake Turkana in northern Kenya. The time interval was the same one the Leakeys had established for
boisei
and
habilis
at Olduvai.
Some of the Koobi Fora specimens clearly represented
boisei,
and for present purposes, they can be placed aside. Others come from something more
Homo
-like, but if they are lumped with the Olduvai
habilis
sample,
habilis
becomes extremely variable. Some individuals (from Koobi Fora) had relatively large skulls and large australopith-size teeth, while others (from both Koobi Fora and Olduvai) had small australopith-size skulls and small
Homo
-sized teeth (Figure 3.7). Brain volume, estimated from eight Olduvai and Koobi Fora skulls, averaged 630
cubic centimeters (cc), but it ranged from a low of 510 cc to a high of 750 cc. The smallest and largest skulls both come from Koobi Fora, and limb bones in the same deposits imply equally large differences in body size. To some specialists, the differences suggest a persistence of the high degree of sexual dimorphism that characterized the australopiths, but to others they indicate that
habilis
actually confounds two species.
The smaller-brained, smaller-toothed species could still be called
habilis,
since it more closely matches the definition that Louis Leakey and his colleagues offered in 1964. Its larger-brained, larger-toothed contemporary would require a new name, for which advocates have proposed
Homo rudolfensis,
based on “Rudolf,” the now obsolete colonial name for Lake Turkana.
If we accept two species, only one could be ancestral to later humans including ourselves, and the choice is not easy. If brain expansion is emphasized, then
rudolfensis
is the clear winner, but if dental and facial reduction are accentuated, then
habilis
is the better candi-date. Limb bones may favor
rudolfensis,
if we assume that some larger isolated thigh bones (femurs) represent this species. In size and shape, 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 84
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0
5 cm
0
2 in
Kenya National Museum -
Kenya National Museum -
East Rudolf Specimen No. 1813
East Rudolf Specimen No. 1470
FIGURE 3.7
Reconstructed skulls of
Homo habilis
from deposits east of Lake Turkana (formerly Lake Rudolf), northern Kenya (redrawn after F. C. Howell 1978, in
Evolution of African Mammals
, Harvard University Press: Cambridge, MA, fig. 10.9). Specialists who want to divide
Homo
habilis
between two species would keep the skull on the left within
Homo habilis
, but they would assign the skull on the right to a new (second) species,
Homo rudolfensis
.
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they closely resemble the thigh bones of later humans, and they suggest that
rudolfensis
was significantly larger than any known australopith. In contrast, two highly fragmentary partial skeletons that are thought to represent
habilis
in the strict sense suggest tiny bodies (one individual may have been no more than 1 meter or 3'3" tall) and arms that may have been remarkably long compared to the legs. Given the australopith-like dentition of
rudolfensis
and the australopith-like body and small brain of
habilis,
some authorities have suggested that they should both be removed from
Homo
and placed in
Australopithecus
. This is ultimately a matter of definition, and an answer won’t help us to decide whether
habilis, rudolfensis,
or both produced the Oldowan tools that occur in the same deposits at Olduvai and Koobi Fora. Unfortunately, for the moment, there is no way to tell, and if they actually were separate species, we can only speculate on how they differed behaviorally and ecologically.
* * *
habilis/rudolfensis
conundrum might be resolved if fossil hunters could recover enough additional bones to determine conclusively how many anatomical or size modes existed 1.9 to 1.6 million years ago. If future discoveries confirmed that there were only two, the implication would be for a single species marked by an extraordinary degree of sexual dimorphism. If new discoveries suggested four modes, we might conclude that there were two species, each predictably with two sexes.
The problem might also be resolved if field workers were to recover additional, more complete skeletons to confirm body size and proportions in one or both species. But these are big “ifs,” and the pace of fossil discovery suggests that they are unlikely to be satisfied soon.
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It’s obviously also crucial to know the history of
habilis/
rudolfensis
before 2 million years ago. In some features of face and brow,
rudolfensis
recalls 3.5-million-year-old
Kenyanthropus platyops,
and if the resemblance implies an ancestor-descendant relationship,
rudolfensis
could be removed from
Homo
to
Kenyanthropus
. This would reduce the puzzling variability in early
Homo,
but there are no fossils between 3.5 and 1.9 million years ago to link
platyops
and
rudolfensis,
and the differences between them in brain size, tooth size, and other aspects are profound. For the moment then, it seems wise to withhold judgment on a possible connection. What is certain is that the line (or lines) that produced
habilis/rudolfensis
were distinct by 2.5 million years ago, because the collateral robust australopith lineage had already emerged by this time.
Unfortunately,
platyops
aside, so far, there are only three fossils that may document
habilis/rudolfensis
before 2 million years ago. These are a skull fragment from Chemeron, Kenya, a lower jaw from Uraha, Malawi, and an upper jaw from Hadar, Ethiopia (Figure 3.8). The Hadar jaw is the most important, because it is more obviously from
Homo
than the Chemeron skull fragment and it is more firmly dated than the Uraha jaw. Potassium/argon analysis of overlying volcanic ash places the Hadar jaw just before 2.33 million years ago, and it resembles
Homo
in multiple features, including its narrowed molars, its limited forward projection (prognathism) below the nasal opening, and the parabolic shape of its dental arcade—the path that the tongue describes as it passes over each tooth beginning with the third molar on one side and ending with the third molar on the other. In the australopiths, the molars tend to be significantly broader, the upper jaw protrudes further forwards below the nose, and the dental arcade is more U-shaped. On the ground near the 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 87
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more U-shaped
dental arcade
more parabolic
dental arcade
0
0
5 cm
2 in
Australopithecus afarensis
Homo
species indeterminate
(Hadar Specimen A.L. 200-1a)
(Hadar Specimen A.L. 666-1)
FIGURE 3.8
Upper jaws of
Australopithecus afarensis
and early
Homo
from Hadar, Ethiopia (drawn by Kathryn Cruz-Uribe from photographs).
jaw, a Hadar team led by William Kimbel found three Oldowan choppers and seventeen flakes that had eroded from the same deposit, and when they excavated they recovered another core tool and thirteen more flakes. They also found fragments of animal bones, including one that bore a possible stone tool mark. So far, the artifacts are the oldest to have been recovered in direct association with a human fossil.
Neither the Hadar jaw nor the other two fossils that may represent
Homo
before 2 million years ago inform on brain size, but if stone flaking and brain expansion were closely linked, then brain expansion must have begun by 2.5 million years ago. Future discoveries may confirm this—or they may not. The
Australopithecus garhi
skull from Bouri, Ethiopia, which we described in the last chapter, provides fodder for doubters. This is because it anticipates
Homo
in its dentition, but not in 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 88
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the enclosure for the brain, which was no larger than in australopiths.
The Bouri deposits have not yielded any stone artifacts, but they have provided animal bones that were cut and broken with stone tools. Unlike nearby Gona, Bouri lacked cobbles or other rock fragments that were suitable for flaking, and when the tool makers visited, they may have carefully conserved their implements until they could return to a locality like Gona. If so, they were thinking ahead in a way that is decidedly human. The bones they damaged include an antelope tibia shaft that was repeatedly cut, bashed, and chopped to get at the marrow, the femur of a three-toed horse that was cut when it was separated from adjacent bones and stripped of flesh, and an antelope lower jaw that was cut on the inner surface when the tongue was removed.
The implication may be, as
Time Magazine
suggested in April 1999, that
garhi
was “the first butcher.” Tim White, whose team found the
garhi
skull and the tool-marked bones, is more cautious: “It’s circumstantial evidence, and not as strong as it might be. It’s possible that some [other] hominid came by and left the tools. Then a year later, a carnivore dropped the carcass of a different kind of hominid [
garhi
]
in the same place.” He continues: “What it tells you, though, is that there was a hominid in these habitats with stone tools [who was]
engaged in large mammal carcass processing. That’s very important.
The behavior is, in some ways, more important than whether it was
garhi
engaging in the behavior.” White calls the bone-processor a
“superomnivore” to distinguish it from its predecessors who were probably more ape-like in both diet and behavior.
White and his team have scoured all the Bouri exposures for fossils and artifacts, and it will be many years, perhaps decades or centuries, before fresh erosion at Bouri provides new clues. Still, there are 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 89
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other like-aged east African sites to explore, and one may yet provide a larger-brained species dated to 2.5 million years ago. The discovery will satisfy those who believe that brain enlargement and stone flaking originated in an evolutionary feedback loop. If
garhi,
however, coexisted with a larger-brained companion, then there must have been at least three distinct human types by 2.5 million years ago—an early robust australopith,
garhi,
and the putative larger-brained species. We could even argue for four types, if we accept, as seems increasingly likely, that
Australopithecus africanus
was restricted to South Africa and disappeared there without issue before 2 million years ago.
In short, the proper metaphor for human evolution between 3
and 2 million years ago may turn out to be a bush, and the high degree of variability in
habilis
/
rudolfensis
between 1.9 and 1.6 million years ago may actually represent the tips of multiple branches that the fossil record will eventually reveal. If there was such a bush, though, natural selection had severely pruned it by 1.6 million years ago, and thereafter only two branches survived—the robust australopiths and the line that ultimately led to ourselves (Figure 3.5). By 1.7 million years ago, this line had produced a species that departed sharply from the australopiths in anatomy, behavior, and ecology, and there is no question about its assignment to
Homo
. Its members have been called the first “true humans,” and we explore next the important step they represent on the long road to human culture.