Sociobiology and cultural materialism

Among the various theories invoked by anthropologists to provide a guiding framework for their discipline, cultural materialism, as expounded by Marvin Harris,10 has some appealing features for a biologist. At the same time, however, it provides another example of my contention that evolutionary biologists have not managed to communicate their message with sufficient clarity to colleagues in related disciplines. I have included the following brief section on cultural materialism in response to Harris's "hope that the advocates of [alternative] strategies will be moved by the possible biases of my interpretations and that they will seek to clarify, if not to change, their positions."

What is the common ground that is shared by evolutionary biology and this school of anthropology? In describing cultural materialism, Harris goes to some length to compare it with other systems of explanation in cultural anthropology. In contrast to most of the alternatives, he asserts that sociobiology and cultural materialism share a "forthright commitment to the general epistemological principles of science, [and] in this respect [they are] natural allies." His approval, however, stops there.

Cultural materialism seeks to identify the causes of cultural choice and diversity first in the infrastructure of human society— the modes of production and of reproduction. Although there are Marxist roots to this system of explanation in its emphasis on the modes of production, Harris justifies it on grounds that need only relatively minor editing to reflect much biological insight:

Like all bioforms, human beings must expend energy to obtain energy (and other life-sustaining products). And like all bioforms, our ability to produce children is greater than our ability to obtain energy for them. The strategic priority of the infrastructure rests upon the fact that human beings can never change these laws. We can only seek to strike a balance between reproduction and the production and consumption of energy."11

This is indeed the fate of a relatively large, long-lived, social, serially reproducing, resource-limited animal. Consequently, it is easy to find merit in a theory of cultural diversity that places primary emphasis on the relations between human populations and the ecological systems in which they exist. For example, cultural materialism postulates that the sizes of bands of hunter-gatherer peoples, their need to adjust local population density seasonally, the nuclear family as a unit of band structure, and features of social organization such as exchange of goods and marriage between bands all flow from the nature and distribution of the resources on which the people live. Similarly, a substantial increase in group size requires an intensified mode of production, such as a shift to agriculture. The opportunity for agriculture based on irrigation leads to large imperial systems more readily than in geographical regions where growing crops depends more immediately on rainfall. And the different pace of evolution of cultures in the Old and New Worlds is postulated to be related to the Pleistocene extinctions of domesticatable ungulates in the western hemisphere. These are but brief allusions to a detailed and thoughtful account of a cultural history whose texture cannot be adequately conveyed in a single paragraph.

Cultural materialism also recognizes, in a vague way, that there are "bio-psychological principles" that drive human behavior and that are shared by other primates. Harris's minimal list is kept as short as he can make it:

1. People need to eat and will generally opt for diets that offer more rather than fewer calories and proteins and other nutrients.

2. People cannot be totally inactive, but when confronted with a given task, they prefer to carry it out by expending less rather than more energy.

3. People are highly sexed and generally find reinforcing pleasure from sexual intercourse—more often from heterosexual intercourse.

4. People need love and affection in order to feel secure and happy, and other things being equal, they will act to increase the love and affection which others give them.12

One can argue about the composition of this list; its existence, however, is tacit recognition that there are some evolutionarily conservative elements to primate behavior. The door is open; evolutionary history is acknowledged.

Harris has been critical of sociobiology, viewing it, like other anthropological theories, as a strictly competitive system of hypotheses. As I indicated above, he enters this discussion because I believe his aim is wide of the mark, and I hope that understanding can be improved by considering his critique in more detail.

His first criticism would be devastating if it had any relevance. Like the remarks of another anthropologist that were quoted at the start of Chapter 4, however, it conveys a view of biology that is a hollow caricature:

The weakness of human sociobiology and all other varieties of biological reductionism arises initially from the fact that genotypes never account for all the variations in behavioral phenotypes. Even in extremely simple organisms, adult behavior repertories vary in conformity with each individual's learning history.13

This would be a weakness only if biologists attributed such authority to genes. They do not, of course, and curiously, Harris actually seems to be aware, for five pages later he writes:

Popular representations of sociobiology have created a false impression of how sociobiologists relate human social behavior to its genetic substrate. Sociobiologists do not deny that most human social responses are socially learned and therefore not directly under genetic control. Wilson. . . has made this point without equivocation: "The evidence is strong that almost but probably not quite all differences among cultures are based on learning and socialization rather than on genes." Richard Alexander. .. has made the same pronouncement: "I hypothesize that the vast bulk of cultural variations among peoples alive today will eventually be shown to have virtually nothing to do with their genetic differences." Thus few if any sociobiologists are interested in linking variations in human social behavior to the variable frequencies with which genes occur in different human populations 14

But let us return for a moment to the passage on the "weakness" of sociobiology. Harris here pays lip service to the fundamental inseparability of the learning process and the evolutionary background on which it occurs, yet he never fully incorporates the significance of this truth into his analyses. Thus genetic and environmental causes are viewed either as alternatives, or the idea that a particular behavior has been molded by evolution is seen as a "redundant and gratuitous" additional hypothesis. These mistakes follow, respectively, from an insufficient appreciation for the complexity of interaction of genetic and epigenetic events as proximate causes of behavior, and a failure to distinguish between the concepts of proximate and ultimate causality. Harris is right to view the evolution of culture in an ecological context, but he is unwise to separate cultural anthropology so remorselessly from evolutionary biology. This is not the path to understanding, for a scientific explanation, however parsimonious, loses all elegance—to say nothing of importance—when it ignores a significant aspect of nature. One can shave too closely with Occam's razor.

Harris's second and third criticisms illustrate these points. The second has to do with the content of the human "ethogram"—with the nature of human nature. While acknowledging that humans have certain species-specific behavioral propensities (which were listed above), Harris would like to keep the list as short and as general as possible. On this matter his disagreement with biology is therefore a quantitative rather than a qualitative issue. His position is tied to that set of traditions in the study of human behavior that assumes there has been no evolutionary channeling of cognition and learning and rejects the hypothesis that certain behaviors are more probable than others because of the evolutionary history of the species. As pointed out above, this position is theoretically unsound because it cuts off the study of cultural evolution from the rest of biology and precludes examination of the problem in every dimension. And it is most easily maintained when the concepts of proximate and ultimate cause become confused, which brings us to Harris's criticism of behavioral scaling.

We have seen earlier that one of the general features of animal behavior is that what animals do frequently depends on the circumstances in which they find themselves. The circumstances, in turn, are made up in various proportions of immediate environmental stimuli, past experience, and evolutionary heritage. Even where there is a large component of genetic programming, the behavioral response is frequently tuned to the specifics of the moment. The concept of behavioral scaling has not been grafted onto the study of human behavior to account in genetic terms for behavioral plasticity. The idea arises in animal behavior from considerations of ultimate cause, but it embodies no specific assumptions about the mechanisms of proximate cause.

The confusion of proximate and ultimate cause is vividly apparent in the following passage:

True, sociobiological models based on reproductive success and inclusive fitness can yield predictions about sociocultural differences that enjoy a degree of empirical validity.. .. But the reason for this predictability is that most of the factors which might promote reproductive success do so through the intermediation of biopsychological benefits that enhance the economy, political, and sexual power and well-being of individuals and groups of individuals Thus sociobiology contributes to the obfuscation of the nature of human social life by its commitment to the exploration of least probable causal relationships at the expense of the most probable. 1S (Emphasis added.)

Without an evolutionary context, "biopsychological benefits" have the same ad hoc character that Harris deplores in the structuralist theories of Levi-Strauss. In fact, they are among the proximate enabling mechanisms through which the genes speak. As Harris implies, the relation between the satisfaction of psychological urges and the "need" or "purpose" of the behavior that produces gratification is frequently very obvious. We take for granted that people must eat and reproduce. But the concept of psychological benefits as proximate enabling mechanisms will be clearer if we consider an example where the "purpose" of the behavior may not be so obvious as our intuition leads us to believe. Consider sleep. When we are deprived of sleep, we feel drowsy—we experience a psychological need for sleep. Moreover, as drowsiness impairs our ability to perform tasks with accustomed facility, and as feeling tired is reversed by sleep, we conclude that the purpose of sleep is to provide a needed period of recovery, a recharging of the batteries. But it is not obvious that this explanation for why we sleep is correct.16 First, people vary greatly in the amount of sleep they require, and some individuals thrive on as little as one hour in twenty-four. Furthermore, if we look at other mammals we find that there is enormous variation: bats may sleep as much as twenty-two hours a day, and many of the large grazing mammals less than three. Is it possible that vertebrates differ so widely in their need for periods of biochemical and physiological recovery? Or is the "purpose" of sleep to synchronize periods of activity with the solar day in a manner that varies with the feeding behavior, sus ceptibility to predation, and other aspects of the ecology of each species? Is hibernation but an extreme form of this behavior? In this view, "it is the sleep control mechanism that makes us feel tired,"17 and we have misinterpreted the meaning of sleep. Feeling drowsy is a proximate enabling mechanism to produce a specific behavior, regardless what purpose we believe the behavior serves.

Let's consider an example with more anthropological interest. It is a delusion to suppose that the wide variation in marriage practices observed throughout the world is evidence that there has been no influence of evolution on human mating behavior. Not all conceivable forms of mating occur, and those that are observed do not occur with equal frequency. When Harris writes that "... people can be socialized into and out of promiscuity, polygyny, polyandry, and monogamy with conspicuous ease, once the appropriate infra-structural conditions are met," he is correctly pointing out that human sexuality has several phenotypic expressions that can be elicited under various conditions. The argument, which is intended to dispose of the notion of a species-specific human mating behavior, does not refute the hypothesis that our species has a significantly polygamous character, uneasily fused together in evolutionary time with powerful, if conflicting, tendencies for pair-bonding. It is probably no accident that monogamous societies have to resort to considerable "socialization" to reinforce their marriage codes, or that rampant promiscuity is not a stable cultural alternative. The argument also does not address the nature of the in-frastructural conditions and how they lead to various mating practices, but in general I suspect that the proximate causes that would be advanced by a cultural materialist would in fact be in harmony with a somewhat broader perspective that sees cultural and biological change frequently interacting in a coevolutionary process. Let us illustrate with a specific example.

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