Gauss Normal Chron

Kaena Reversed Subchron Mammoth Reversed Subchron

Gilbert Reversed Chron

Cochiti Normal Subchron I Nunivak Normal Subchron

Sidufjall Normal Subchron I Thvera Normal Subchron

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.

Artifacts resembling those from Gona have been dated to 2.4 to 2.3 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.

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 "pro-tobiface," and protobifaces graded into true bifaces (or hand axes) on which the flaking covered both surfaces. Bifaces are unknown in the

Biface Manufacture

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).

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.

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 crescent 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.

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 containing 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 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.

Oldowan tool makers did much more than flake stones. At Gona, Koobi Fora, Olduvai, and other sites, they accumulated the flakes and core forms in clusters that mark the world's oldest known archeolog-ical sites. Where soil conditions were favorable, the clusters also preserve fragmentary animal bones. The bones commonly come from antelopes, zebras, pigs, and other animals that are far larger than any on which chimpanzees feed, and it is tempting to regard each cluster as a campsite where Oldowan people converged each night to exchange food, have sex, or simply socialize, just as modern hunter-gatherers often do. Such an interpretation may be too far-reaching, however, and the clusters could represent something far more prosaic, like clumps of trees in which individuals congregated to feed in safety. So far, no cluster has provided unequivocal traces of fireplaces or of structures that would imply anything more.

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 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.

At this point, the reader is surely wondering just who these Oldowan people were. What species did they belong to and what did they look like? To address this question, we must return briefly to the australo-piths and their evolutionary history. Anthropologists disagree on the relationships among the austral opith species that existed before 2.5 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 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 aus-tralopith 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 aus-tralopiths 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, boi-sei, 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

Homo millions of neanderthalensis years ago 0

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