BUTCHERY AND THE SCAVENGING HYPOTHESIS IN PREHISTORY

Langerie- France

During the 1970s and 1980s, when the debate over the relative importance of gathering and hunting was gaining momentum, there was virtually no evidence of plant use by early hominins. It is correct that this absence of evidence was not generally regarded as evidence of absence – organic materials just have a habit of quickly decomposing in most climates. The situation is somewhat different for remnants ofanimals, such as bones, which have the potential to be preserved for millions of years through drying or mineralization. When the right conditions exist, such bone accumulations are exposed or buried in deposits shallow enough to allow discovery. When they are found mingled with the crude stone tools used by early hominins, they reveal how meat may have been obtained, processed, and perhaps shared.
Fracture patterns and tool marks on bones provide unequivocal evidence that animal carcasses were being butchered. The tools found in association with bones of large mammals are generally classed as Oldowan, from Olduvai Gorge, where they were first recovered. The hallmark Oldowan tool is a cobble sharpened on one end to produce a rough edge for cutting. Other stones show signs of battering, as if they had been used to break open bones to obtain fat-rich marrow. Clearly these animals were on the hominin menu; there is no other reasonable explanation for the behaviors indicated by the “bone beds” of Olduvai and other African sites.
How these carcasses arrived at their resting place, however, is a separate issue and one that is trickier to investigate. If not hunting, then what? The scavenging hypothesis emerged as the chief alternative to the “Man the Hunter” model. After all, the African grasslands today are littered with carcass remnants left by top carnivores such as lions. After they have their fill, hyenas, wild dogs, carrion birds, and others take their turn at what remains: bones (some with marrow), scraps of flesh, and perhaps some viscera. Perhaps early hominins created their
own niche by scavenging such kills during the middle of the day, when most animals were resting. For this to be a successful strategy, however, there had to be enough nutritional value left in these carcasses to make their exploitation worthwhile. More might be gained by actively driving away carnivores and other scavengers and appropriating their kills while they were still meaty.
Whether or not a scavenging adaptation was feasible is a question that is still being debated. Relevant evidence continues to accumulate, but is not always easy to interpret as supportive of either hunting or scavenging. Instead, it is becoming apparent that meat acquisition by early hominins probably ranged along a continuum from passive versions (picking at long-abandoned kills) to more active ones, such as theft or hunting. Sometimes a sequence of behaviors can be deciphered from the order in which the bones were subjected to various actions, such as cutting, crushing, and gnawing by carnivores. The distinctive markings that characterize different treatments have been identified experimentally and the knowledge transferred to the interpretation of hominin butchering sites. Microscopic examination can detect which activity came first, as when cut marks are overlain by tooth marks.
These studies show that in some cases at least, hominins had early access to the carcass, perhaps after predators had done some damage but before hyenas and other scavengers could fragment and disperse the bones. Further doubt is cast on the passive scavenger model by the fact that many sites preserve high frequencies of undamaged long bones – these prizes would surely haven been cracked open by tool-using hominins who arrived at the kill too late to partake of the meatier parts of the carcass. Our small-brained hominin ancestors may not have been sprinting across the plain, spears in hand; they were nonetheless active in the pursuit of game using a variety of strategies. Australopithecines probably preyed on small animals, much as chimpanzees do today. Larger game was certainly consumed, but in order for this to be a successful strategy, it must have involved early access to carcasses before predators or other scavengers could eat their fill.

A CLOSER LOOK AT THE FOSSIL RECORD

Like a crime scene, a site of butchering by early hominins offers analysts an opportunity to reconstruct, systematically and scientifically, the events that created it. However, such re-creations are necessarily circumstantial. For direct evidence of what these hominins actually ate, we must turn to the nutritional equivalent of gunpowder residue: the traces of food and eating that become part of the body. For such ancient fossils, chemical and mechanical traces of this kind are rare, and when available, they are often difficult to interpret. Nonetheless, they are invaluable tools for documenting diet because they provide a record of actual consumption, not just the activities involved in obtaining and preparing food.
We all carry in our bodies a record of what we eat. Substances that we ingest are broken down into more basic components, and these particles are then used to build and repair tissues, as well as being metabolized to yield energy. As animals, we take in large quantities of common organic elements, such as carbon and nitrogen. More important for the paleoanthropologist, however, are the rarer variants of elements that occur only as a minute percentage of the total found in the global environment. These isotopes differ from their more common versions only in the number of neutrons in their nuclei, but this minor variation is sufficient to cause them to behave differently in chemical reactions. Some isotopes are radioactive, such as carbon-14 (14C), widely known as a dating tool. Others are stable (nonradioactive), among them the isotopes of carbon and nitrogen that have known concentrations in different food sources.
Both isotopes and nonisotopic elements leave characteristic signatures as they are metabolized by organisms. Studies of early hominin diet have relied heavily on ratios of strontium (Sr) to calcium (Ca). Diets rich in plant material build bones that have a high Sr/Ca ratio compared to those that emphasize animal foods. This means that the Sr/Ca ratio gets lower as we go up the food chain from primary producers (plants), to herbivores, and finally to the top carnivores that eat only other animals. Another indicator of diet is the stable isotope of carbon known as 13C. The ratio of 12C (the common garden variety carbon) to 13C can vary greatly among the kinds of plants that form the base of the food chain. Plants, particularly grasses, that have adapted to arid conditions sometimes use a variant metabolic pathway that causes them to accumulate relatively high proportions of 13C (confusing for the nonchemist, they are called C4 plants for the number of carbon atoms produced at a crucial stage of photosynthesis). The same goes for animals that eat those C4 plants and the predators that consume them, all the way up the food chain. What these chemical profiles reveal is that early hominins relied heavily on plant foods, mostly seeds and tubers rather than fleshy fruits, with some insects and small animals mixed in. Teeth of South African australopithecines are relatively high in 13C, suggesting a diet rich in drought-tolerant C4 plants or the animals that eat them. It is estimated that these hominins got 25 to 35 percent of their calories from C4 sources.9 Certainly this would make sense in the context of forest fragmentation and expansion of grasslands; C3 plants, including most fruit-producing trees, were becoming harder to locate and farther apart. What kinds of foods are responsible for this C4-enriched diet? Grass seeds? Perhaps; however, grass grains are generally low quality resources, meaning that they contain a great deal of indigestible fiber and, thus, have low nutritional value.
There are some other possibilities, however. Many sedges, typically found in wetlands, are also C4 plants and have nutritious tubers. Some small mammals, such as cane rats and hyraxes (rodent-like relatives of elephants), subsist mainly on C4 plants, as do grasshoppers and many termites. Fishing for termites is something that chimpanzees do using bits of straw or sticks to coax them out of their nests, and australopithecines were capable of performing this task as well. None of these C4-enriched foods alone can account for the chemical profile of early hominin teeth, but in combination they certainly would. Australopithecines were branching out from a heavily fruit-based diet to one much more attuned to a varied landscape mosaic of dense forest, grasslands, woodlands, and wetlands.
The Sr/Ca ratio of South African australopithecines is also rather high, similar to that of grazers and carnivores on the African savannah today and much higher than that of browsers. This result seems to suggest that these hominins were eating grass or the herds of hoofed animals that fed on it. However, there are other foods consistent with the observed Sr/Ca ratios that provide a better fit with the general trend of primate diets and are well within the capabilities of animals with a rudimentary technology. These include insects and small mammals such as hyraxes, which also match nicely with the 13C data. Underground storage organs also are enriched in strontium – although, being in most cases the product of C3 plants, they diverge from the trend indicated by stable carbon isotopes.
These issues are not yet resolved, and isotope studies are still relatively new to paleoanthropology. However, it seems safe to say that there is nothing in the chemistry of australopithecine teeth that indicates a meat-rich diet. Instead, the early hominin strategy was one that took advantage of a variety of habitats and food sources, rather than specializing in one or a few of them, setting the stage for the even greater versatility that was still to come.
While accumulating a chemical record of diet, teeth are also suffering wear and tear from chewing. When studied at the microscopic level, they show distinctive patterns of wear depending on the type of foods eaten. The silica particles in grasses carve out grooves in the enamel, leaves produce scratches, and fruits cause pitting. Tooth wear in australopithecines indicates a diet of seeds and soft fruits initially, with the addition of more brittle or tough foods as diets became more varied. The surface of hominin teeth, thus, tells the same story as the molecules within them, one of being versatile enough to rewrite the menu to utilize the available ingredients.

By Kristen J. Gremillion in the book "Ancestral Appetites" - Food in Prehistory, Cambridge University Press, New York, 2011, excerpts p.18-22. Adapted and illustrated to be posted by Leopoldo Costa. 

ABOUT THE BOOK

ANCESTRAL APPETITESThis book explores the relationship between prehistoric people and their food – what they ate, why they ate it, and how researchers have pieced together the story of past foodways from material traces. Contemporary human food traditions encompass a seemingly infinite variety, but all are essentially strategies for meeting basic nutritional needs developed over millions of years. Humans are designed by evolution to adjust our feeding behavior and food technology to meet the demands of a wide range of environments through a combination of social and experiential learning. In this book, Kristen J. Gremillion demonstrates how these evolutionary processes have shaped the diversification ofhumandiet over several million years of prehistory. She draws on evidence extracted from the material remains that provide the only direct evidence of how people procured, prepared, presented, and consumed food in prehistoric times. Kristen J. Gremillion is an Associate Professor in the Department of Anthropology at The Ohio State University. She has published many articles on human dietary variability in journals including "American Antiquity", "Current Anthropology", and "Journal of Archaeological Science" as well as chapters in several edited volumes.