Having described the fossil material, we may now consider how evolution transformed an early ape into a hominin. Generally, such paleoanthropological reconstructions and hypotheses about the origin of bipedalism rely heavily on the evolutionary role of natural selection. The question at hand is not so much why bipedalism developed as much as how bipedalism allowed these ancestors to adapt to their environment.
Hypotheses about adaptation begin with features evident in the fossil evidence. For example, the fossil record indicates that once bipedalism appeared, over the next several million years the shape of the face and teeth shifted from a more apelike to a humanlike condition. To refine their hypotheses, paleoanthropologists add to the fossil evidence through scientific reconstructions of environmental conditions and inferences made from data gathered on living nonhuman primates and humans. In this regard, evolutionary reconstructions involve piecing together a coherent story or narrative about the past. Sometimes these narratives are tenuous. But as paleoanthropologists consider their own biases and incorporate new evidence as it is discovered, the quality of the narrative improves.
For many years, the human evolutionary narrative has been tied to the emergence of the savannah environment in eastern Africa as the global climate changes of the Miocene led to increasingly cooler and dryer conditions. While the evidence from Ardipithecus shows that the earliest members of the human line were forest dwellers, over time the size of tropical forests decreased or, more commonly, broke up into mosaics where patches of forest were interspersed with savannah or other types of open country. The forebears of the human line are thought to have lived in places with access to both trees and open country. With the breaking up of forests, these early ancestors found themselves spending more and more time on the ground and had to adapt to this new, more open environment.
The most obvious problem facing these ancestors in their new situation, other than getting from one patch of trees to another, was getting food. As the forest thinned or shrank, the traditional ape-type foods found in trees became less available, especially in seasons of reduced rainfall. Therefore, it became more and more necessary to forage on the ground for foods such as seeds, grasses, and roots. With reduced canine teeth, early bipeds were relatively defenseless when down on the ground and were easy targets for numerous carnivorous predators. That predators were a problem is revealed by the South African fossils, most of which are from individuals that were dropped into rock fissures by leopards or, in the case of Dart’s original find, by an eagle.
Many investigators have argued that the hands of early bipeds took over the weapon functions of the reduced canine teeth. Hands enabled them to threaten predators by using wooden objects as clubs and throwing stones. This quality is shared with many of the other hominoids. Recall the male chimpanzee (Chapter 4) who wielded objects as part of his display to obtain alpha status. In australopith-ecines the use of clubs and throwing stones may have set the stage for the much later manufacture of more efficient weapons from bone, wood, and stone.
Although the hands of the later australopithecines were suitable for tool making, no evidence exists that any of them actually made stone tools. Similarly, experiments with captive bonobos have shown that they are capable of making crude chipped stone tools, but they have never been known to do so outside of captivity. Thus to be able to do something is not necessarily equivalent to doing it.
In fact, the earliest known stone tools, dating to about
2.5 mya, are about 2 million years more recent than the oldest fossils of Australopithecus. However, Australopithecus certainly had no less intelligence and dexterity than do modern great apes, all of whom make use of tools when it is to their advantage to do so. Orangutans, bonobos, chimpanzees, and even gorillas have all been observed in the wild making and using simple tools such as those described in Chapter 4. Most likely, the ability to make and use simple tools is something that goes back to the last common ancestor of the Asian and African apes, before the appearance of the first bipeds.
It is reasonable to suppose, then, that australopithecine tool use was similar to that of the other great apes. Unfortunately, few tools that they used are likely to have survived for a million and more years, and any that did would be hard to recognize as such. Although we cannot be certain about this, in addition to clubs and objects thrown for defense, sturdy sticks may have been used to dig edible roots, and convenient stones may have been used (as some chimpanzees do) to crack open nuts. In fact, some animal bones from australopithecine sites in South Africa show microscopic wear patterns suggesting their use to dig edible roots from the ground. We may also allow the possibility that, like chimpanzees, females may have used tools more often to get and process food than males, but the latter may have used tools more often as “weapons.”98 The female chimpanzees who hunted with spears as described in Chapter 4 call into question these distinct roles for the sexes.
World History
