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.
Early Hominid Environment and Ecology
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 Seasonality
The 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:- 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 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.
Archaeological Evidence
Much of the archaeological evidence also points to a shift in dietary composition, although direct evidence of meat eating is rarely found. Insted, meat eating has been inferred from many different sources. One source is through the interpretation of presence and quantity of different skeletal elements found in living floors (supposed places of hominid 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 has not been adequately investigated. Accumulations of bones and stone tools, while intriguing as evidence of hominid 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 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.
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Additional interpretations can also be carried out concerning the timing and sequence of resource acquisition by examining which marks come first. Assessing which marks (when marks from both carnivore teeth and hominid tools are present) lie below and above can be crucial for interpreting meat-eating behavior of early hominids. Were they hunters, or merely scavengers of the remains of prey felled by larger carnivores? The available evidence suggests that early hominids engaged in both activities, although the evidence for hunting and primary access to meat resources increases in later levels (especially with Homo erectus). The impacts of this behavioral change on the development and evolution of hominid social organization have been profound, particularly in the realm of cooperation within social groups. |
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