Chapter twelve: oldowan toolmakers and the origin of human life history

Chapter Review

The Oldowan Toolmakers

The earliest stone tools—large, rough-hewn pebbles called Oldowan tools—appear in the fossil record at about 2.5 mya. The variety of hominin-modified artifacts suggests that earliest toolmakers were already quite skilled. It is probable, then, that hominins were crafting tools out of less durable material long before they learned how to chip at stone. The archaeological sites from which these tools come are crucial to our understanding of the shifts in life histories and behavioral patterns that gave rise to the later hominin lines.

Reconstructing Ancestral Life Histories

Finding out what early hominins actually did and how they acted are tricky tasks, particularly since it is difficult to imagine what the landscape might have been like hundreds of thousands—or even millions—of years ago. While the fragmentary remains of the past are ingeniously interpreted by researchers, additional information is often required to corroborate some of the conjectures that arise. Researchers can use inferences drawn from animal studies, especially those of the African great apes (i.e., gorillas, chimpanzees, and bonobos). While none of the ape models is expected to provide an exact replica of hominin behavior (since apes themselves are derived forms with their own evolutionary and behavioral histories), the likelihood of hypothesized models can be tested through field observation. Consistent approaches by a majority of primate groups to particular ecological dilemmas strongly suggests that a specific response could be a likely scenario in hominin evolution as well.

Comparison using contemporary hunter-gatherers draws on human behavioral variation through the study of different cultures. Again, while no existing societies are expected to conform to an exact hominin lifestyle (no modern humans living today are evolutionary throwbacks—they have their own distinct cultural and political histories), many insights have arisen through the study of human foraging societies. The fact that there appear to be many commonalities between culturally different foraging societies suggests that ecological constraints may provoke similar responses from different people.

Complex foraging among Hominins

Early theories of hominin evolution relied almost solely on the idea that hunting and meat-eating (see below) were and are exclusive to humans and our ancestors. We now know, however, that chimpanzees regularly hunt and eat monkeys, and that our ancestors may have foraged for many different sorts of resources. The study of the kinds of skills contemporary peoples use during foraging activities coupled with archaeological evidence suggests that early hominins may have had a wide knowledge of their environment and the resources they could exploit.

Human forages typically combine extractive foraging (acquiring food that must be processed in some way before it can be eaten, like nuts with hard shells and tubers) with hunting, skills that require years of practice to hone. In contrast, when chimpanzees forage, they almost solely rely on collected foods, those that may simply be picked and eaten. Hominins may have evolved larger brains and a longer period of juvenile development to adapt to the rigors of a complex foraging lifestyle.

Meat-Eating, Cooperation, and Seasonality

The inclusion of meat in the hominin diet has long been cited as a prominent factor in the evolution of human-like social organization. From a more contemporary functional ecological perspective, however, meat is a precious commodity for modern foraging groups, providing a bonanza of calories and proteins that are otherwise difficult to acquire. Even so, the desirability of meat obscures the reality of day-to-day existence: Hunting parties, more often than not, return empty-handed. Bearing that in mind, there are two factors that make a system of food sharing desirable, if not absolutely necessary, for relying on meat in the diet to be feasible:

High payoff for success: Success often brings enough food for the entire social group.
Low individual success rate: Successful hunts are likely unpredictable and irregular, making success for any individual hunter relatively low at a particular point in time.

These conditions suggest that a network of food sharing would greatly benefit all participating parties by providing a buffer against starvation (or malnutrition) due to individual irregularities in success. Such a system would be an obvious example of reciprocal altruism, in which individuals who did not participate in food sharing were rapidly excluded from subsequent events.

An additional factor influencing the increasing amounts of meat in the hominin diet may have been accentuated seasonality in the environment. The dry season decreased resource variety and abundance, causing many animals to divert their foraging strategies to exploit more of a single food item or a greater variety of foods they may not have sought out before. These might include underground storage organs and nuts from plants and other specialty food items to compensate for an overall decrease in resource abundance. Robert Foley (Cambridge University) proposed that during human evolution, two modes of adaptation were exercised by the hominins. The paranthropines developed masticatory specializations that allowed them to exploit tougher plant materials, while the australopithecine species relied on a diversified diet, which included more seasonal meat consumption.

Archaeological Evidence and the Oldowan Toolmakers

Much of the archaeological evidence also points to a shift in dietary composition, although direct evidence of meat-eating is rarely found. Instead, meat-eating has been inferred from many different sources. One source is through the interpretation of the presence and quantity of different skeletal elements found in living floors (supposed places of hominin occupation). High densities of bones found in association with stone tools have led researchers to believe that processing and consumption of carcasses took place at these sites. However, interpretation of this information can often be misleading, particularly if taphonomy (the study of how archaeological sites are formed) has not been adequately investigated. Accumulations of bones and stone tools, while intriguing as evidence of hominin meat-eating, could also be the result of unrelated processes. Careful examination of the surrounding matrix is required to determine depositional integrity.

Sites from Olduvai Gorge examined in this manner suggest that site accumulation was not a by-product of river deposition. A number of the bones accumulated in the Olduvai Gorge sites exhibit evidence of cut marks made by stone tools. Although it may be difficult to distinguish between tool-derived cut marks and other possible agents of bone modification (for example, carnivore tooth marks) with the naked eye, examination under high magnification shows a clear distinction between the two. Grooves produced by tools often leave many smaller, parallel grooves in the main cut, whereas carnivore marks tend to be broad, smooth grooves on the bones. (Figs. 12-1 and 12-2).

6-1

Figure 12.1 Difference in patterns of marks on bone produced by a stone tool and by a tooth.
Image Credit: W.W. Norton.

6-1

Figure 12.2 Male lions feeding.
Image Credit: Robert Boyd and Joan Silk.

Additional interpretations can also be arrived at concerning the timing and sequence of resource acquisition by examining which marks come first. Assessing which marks (when marks from both carnivore teeth and hominin tools are present) lie below and above can be crucial for interpreting meat-eating behavior of early hominins. Were they hunters or merely scavengers of the remains of prey felled by larger carnivores? The available evidence suggests that early hominins engaged in both activities, although the evidence for hunting and primary access to meat resources increases in later levels (especially with Homo erectus). The effects of this behavioral change on the development and evolution of hominin social organization have been profound, particularly in the realm of cooperation within social groups.

Back to Top