Chapter 12: The Lives of Early Hominids
Reconstructing Ancestral Lifeways Using Humans and Non-Human Primates
Finding out what early hominids actually did and how they acted is a tricky task, particularly since it is difficult to imagine what the actual landscape might have been like hundreds of thousands - or even millions - of years ago. While the fragmentary remains of the past are often ingeniously interpreted by researchers, additional information is often required to corroborate some of the conjectures which arise. Two additional ways in which ancestral pathways are examined rely upon ethographic and ethnographic comparison.
Ethographic comparison relies upon inferences drawn from animal studies, especially those of the African Great Apes (i.e., gorillas, chimpanzees and bonobos). While none of the ape models are expected to provide exact replicas of hominid behavior (since apes themselves are very derived forms), the likelihood of some models can be tested through field observation. Consistent approaches by a majority of primate groups to particular ecological dilemmas strongly suggests that response to be a likely scenario in hominid evolution as well.
Ethnographic comparison draws upon human behavioral variation through the study of different cultures. Again, while no existing societies are expected to conform to an exact hominid lifestyle (no modern humans living today are evolutionary throwbacks), many insights have been made through the study of hunter-gatherer social groups. The fact that there appear to be many commonalities between culturally different hunter-gatherer societies suggests that ecological constraints often provoked similar responses from different people in the past.
Paleoecological reconstruction is possible through the study of correlates to environment and ecology. Plants and animals which existed in particular types of environments are carefully extracted and catalogued as fluctuations inthe biosphere over a period of time. Added to this is the use of oxygen isotopes, which indicate worldwide temperature fluctuations. More recently, analysis of aeolian (wind) dust deposition has provided a more detailed record of climate change and seasonality. All of these forms of evidence point towards an increasingly cold and dry environment with greater seasonality during the late Miocene and Pliocene eras. Reduction in forested areas most likely spelled to end for many Miocene hominoid species. The hominids successfully adapted to open savanna and woodland environments, developing a series of different strategies for predator defense, foraging, and social behavior. One of these behavioral adaptations was possibly a shift to accomodate quantities of meat in the diet, to augment plant resources.
Meat Eating, Cooperation, and SeasonalityThe inclusion of meat in the hominid diet has long been cited as a prominent factor in the evolution of human-like social organization. Many of the earlier theories took this concept and ran with it, from Robert Ardrey's portrayal of the Killer Ape, to the "sanguinary habits" which convinced Raymond Dart of our evolutionary history of bloodlust. From a more contemporary functional ecological perspective however, meat is a precious commodity for modern hunter-gatherers, providing a bonanza of calories and proteins which are otherwise difficult to acquire. The desirability of meat, however, obscures the reality of day-to-day existence: hunting parties, more often than not, return emptyhanded. Bearing that in mind, there are two factors which make a system of foodsharing desirable - if not absolutely necessary - for a reliance on meat in the diet to be feasible:
These conditions suggest that a network of foodsharing 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, where individuals who did not participate in foodsharing were rapidly excluded from subsequent events.
An additional factor influencing the increasing amounts of meat in the hominid 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 in plants, nuts, or 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 hominids. The robust Australopithecines developed masticatory specializations which allowed them to exploit tougher plant materials, while the more gracile species relied upon a diversified diet - which included more seasonal meat consumption.
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 cutmarks made by stone tools. While it may be difficult to distinguish between tool-derived cutmarks and other possible agents of bone modification (e.g., carnivore toothmarks), 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 smooth throughout the trough.