The Dawn of Human Culture (8 page)
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Fossil and artifact hunters look for places where fossils or artifacts have eroded from ancient deposits. When they find what they are seeking, they first attempt to establish the layer of origin, and if the layer remains intact nearby, they often excavate to recover objects that are
“
in situ,
” that is, still sealed in their original resting places.
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The most ancient artifacts come from the drainage of the Gona River, a tributary of the Awash, between Hadar on the north and Bouri and Aramis on the south (Figure 3.1). Rutgers University archeologist Jack Harris made the first discovery in 1976, but it was only between 1992 and 1994 that a team including Harris and his Ethiopian colleague, Seleshi Semaw, excavated a large number of pieces
in situ
and firmly established their geologic age. The excavated sample numbers more than 1000 pieces from two separate sites, and it is supplemented by about 2000 pieces that had eroded onto the surface near to the excavations.
For raw material, the Gona artifact makers selected volcanic pebbles or cobbles from ancient streambeds, and they left behind sharp-edged flakes, the faceted “cores” from which the flakes were struck, and the battered “hammerstones” that were used to strike the cores. The Gona people clearly understood that to obtain flakes routinely, they had strike the edge of a core forcefully at an oblique angle.
When a flake is removed this way, it usually exhibits a distinct swelling or “bulb of percussion” on the inner surface immediately adjacent to the point of impact or “striking platform.” Archeologists rely heavily on bulbs to distinguish human flaking from natural fracturing, since collisions between rocks in a stream or under a waterfall tend to be more glancing, and the fracture products rarely show distinct bulbs.
The Gona flakes regularly do (Figure 3.2), and they come from silty, low-energy floodplain deposits where natural collisions were unlikely to occur. Their origin as artifacts is thus assured.
The geologic antiquity of the Gona artifacts has been equally well fixed by a combination of potassium/argon and paleomagnetic dating. The potassium/argon method shows that a volcanic ash above 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 66
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Hadar
Gona (Middle
Awash)
Omo Koobi Fora
Lokalalei
(West Turkana)
Equator
ift
Chemeron
Rn
Olduvai Gorge
r e t s e W
Eastern Rift
Atlantic
Uraha
Ocean
Sterkfontein &
Swartkrans
Indian
Ocean
FIGURE 3.1
Locations of the sites with Oldowan tools, fossils of early
Homo
, or both mentioned in the text.
the tool-bearing layer accumulated just before 2.5 million years ago.
The paleomagnetic method relies on the repeated tendency of Earth’s magnetic field to flip 180 degrees, meaning that the direction a compass needle would point has periodically shifted from north to south and back again. Iron particles in volcanic rocks and in fine-grained sediments like those at Gona retain the ancient direction of the field, 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 67
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and the global sequence of shifts has been dated in volcanic rocks (Figure 3.3). Geophysicists use the term “normal” to refer to a time interval when the magnetic field was oriented north as it is today and
“reversed” to refer to an interval when it was oriented south. The Gona deposits record a north-to-south shift just below the tool layer, and such a flip is known to have occurred 2.6 million years ago. Together, then, potassium/argon and paleomagnetism bracket the Gona artifacts between 2.6 and 2.5 million years ago.
flake
flake
striking
bulb of
platform percussion
bulb of
striking
percussion
platform
flake
bulb of
striking
percussion
platform
0
5 cm
core (irregular discoid)
0
2 in
Oldowan artifacts from Gona, Ethiopia
FIGURE 3.2
Oldowan artifacts from the Gona site, Middle Awash Valley, Ethiopia (redrawn after S. Semaw 2000,
Journal of Archaeological Science
27, fig. 8).
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millions of
years ago
polarity
0.1
0.3
Brunhes Normal Chron
0.5
0.7
0.9
Jaramillo Normal Subchron
1.1
1.3
1.5
Matuyama Reversed Chron
1.7
1.9
Olduvai Normal Subchron
2.1
Réunion I Normal Subchron
2.3
Réunion II Normal Subchron
2.5
Gona
2.7
Gauss Normal Chron
2.9
3.1
Kaena Reversed Subchron
3.3
Mammoth Reversed Subchron
3.5
3.7
3.9
Gilbert Reversed Chron
4.1
Cochiti Normal Subchron
4.3
4.5
Nunivak Normal Subchron
4.7
Sidufjall Normal Subchron
4.9
Thvera Normal Subchron
5.1
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Older artifacts may exist, but southern African and other eastern African sites indicate that they cannot be much older. Deposits that are about 2 million years old at the
robustus
cave of Swartkrans in South Africa contain flaked stone artifacts, but deposits dated between roughly 3 million and 2.5 million years ago at the
africanus
caves of Sterkfontein and Makapansgat do not. Similarly, deposits at Hadar with abundant remains of
afarensis
dated between 3.4 and 2.8 million years ago have produced no artifacts, but a younger site dated to 2.33 million years has. This younger site is particularly important, because it has also provided a fossil that may represent the artifact maker.
Together, observations in South Africa, at Hadar, and at other east African sites indicate that the Gona date of 2.6 to 2.5 million years ago must closely approximate the actual time when stone flaking began.
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million years ago at Hadar, at Omo just north of Lake Turkana in southern Ethiopia, and at Lokalalei west of Lake Turkana in northern Kenya.
Similar artifacts also occur at eleven east and South African localities that date between 2 million and 1.7 to 1.6 million years ago. The South African artifacts come from Swartkrans Cave and from deposits at Sterkfontein Cave that overlie those with
africanus
fossils. The most
FIGURE 3.3
The global geomagnetic stratigraphy for the past 5 million years and the geologic age of the Gona site. Black rectangles designate past intervals when polarity was normal, white rectangles intervals when it was reversed. Geophysicists refer to long intervals of normal or reversed geomagnetic polarity as chrons and to shorter intervals as subchrons.
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important east African sites are at Koobi Fora on the eastern shore of Lake Turkana and at Olduvai Gorge in northern Tanzania. As a group, the east and South African sites show that artifact technology remained remarkably stable for nearly a million years after it began.
The Olduvai artifact assemblages are particularly large and thoroughly described, thanks again to the dedication of Louis and Mary Leakey. Archeologists group similar stone tool assemblages within an
“Industry,” an “Industrial Complex,” or a “Culture,” and Louis suggested the name Oldowan Industry to encompass the most ancient Olduvai artifacts. Since all other assemblages before 1.7 to 1.6 million years ago closely resemble those from Olduvai, they are now also assigned to the Oldowan. In Mary Leakey’s pioneering descriptions of Oldowan tools, she made a basic distinction between core forms shaped by the removal of flakes and the flakes themselves. She then divided both core forms and flakes among different types depending mainly on size, shape, and the degree of working (Figure 3.4). Thus, she used the term “scraper” for a flake that had been modified (or “retouched”) by the removal of yet additional, smaller flakes on one or more edges. She distinguished between small scrapers, which she called “light duty,” and large scrapers, which she called “heavy duty.” She divided core forms between “choppers,” on which flaking was restricted to one edge, and “discoids,” “spheroids,”
and “polyhedrons,” on which flaking was more extensive and produced pieces shaped like discs, spheres, and cubes. Choppers could be either
“unifacial,” with the flaking restricted to just one surface, or “bifacial,”
with the flaking spread out over both surfaces. A “bifacial chopper” on which the flaking extended around the entire periphery became a “protobiface,” and protobifaces graded into true bifaces (or hand axes) on which the flaking covered both surfaces. Bifaces are unknown in the 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 71
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hammerstone
subspheroid
core scraper
bifacial chopper
flake scraper
polyhedron
flake
0
5 cm
0
2 in
Oldowan tool types
discoid
FIGURE 3.4
Representative types of Oldowan stone tools recognized by Mary D. Leakey and other specialists (redrawn after originals by Isaac and J. Ogden in N. Toth 1985,
Journal of Archaeological
Science
12, fig. 1).
Oldowan proper, but they are the hallmark of the subsequent Acheulean Industry which emerged from it about 1.7 to 1.6 million years ago.
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Specialists have sometimes defined yet further tool types or subtypes, but even the basic list probably exaggerates the formality of Oldowan assemblages. Anyone who has tried to sort Oldowan tools knows that many fail to conform to predefined types. Individual pieces often have attributes of two or more types, and they can be pigeonholed only after much subjective head-scratching. Gary Larson captured the essence of the problem in a cartoon showing an early human trying to crack a boulder with a roughly shaped stone. In exasperation, the would-be boulder breaker turns to his tool-box-toting assistant and says, “So what’s this? I asked for a hammer! A hammer! This is a cres-cent wrench. Well, maybe it’s a hammer. Damn these stone tools.”
Archeologist Nicholas Toth of Indiana University has conducted experiments that explain why attempts to pigeonhole Oldowan tools are so frustrating. Toth is skilled at stone flaking, and his efforts to replicate Oldowan core forms show that their final shape depends not on a template in the maker’s head, but on the shape of the raw pebble or other unmodified rock fragment with which the maker starts.
The result is that experimental products tend to intergrade in shape, just like genuine Oldowan core forms.
Archeologists have often assumed that Oldowan people were more interested in core forms than in flakes, but Toth believes that the core forms were mainly byproducts of flake manufacture. Butchering experiments show that heavier core tools with long cutting edges and large gripping surfaces can be useful for dismembering large carcasses or for smashing bones to get marrow. But for entering a carcass and removing muscle masses, nothing that Oldowan people made could surpass a fresh lava or quartz flake. And when a flake became dull from use, a butcher could always strike a fresh one and continue on.
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Cut-marked animal bones demonstrate that Oldowan people often employed stone flakes just as Toth proposes. In their stone working, they mainly focused on sharp edges, and they probably cared little about the final shape of the core.
By later human standards, Oldowan stone-working technology was remarkably crude, and an observer might reasonably ask if it exceeded the capability of a chimpanzee. The answer is probably yes, based on research that Toth and his colleagues have done with Kanzi, a bonobo at the Yerkes Regional Primate Center in Atlanta, Georgia.
(Bonobos differ from “common” chimpanzees in body proportions and in aspects of social behavior. They are geographically separated from common chimpanzees in the wild, and they are usually placed in a separate species, although they readily interbreed with common chimpanzees in captivity.) When Kanzi was still an infant, psychologist Sue Savage-Rumbaugh and her colleagues began to investigate his ability to communicate with symbols, and they found that he was an unusually talented subject. Toth had taught scores of students to make stone tools, and he reckoned that if he could teach any ape, Kanzi was the one. In the spring of 1990, when Kanzi was nine years old, Toth showed him how to strike a sharp stone flake from a core and how to use the flake to sever a nylon cord encircling a box contain-ing an edible treat. Kanzi got the point immediately, but he had great difficulty producing flakes in the standard human way by striking a core with a hammerstone. In his frustration and perhaps to his credit, he soon devised an alternative method: hurling a core against a concrete floor.
Kanzi sometimes did obtain the sharp-edged pieces he needed, but even after months of practice, neither his cores nor his flakes came 03 Whodunit.r.qxd 1/29/02 5:04 PM Page 74