The term sociobiology (behavioral ecology and evolutionary ecology are synonyms) refers broadly to the application of the principles of Darwinian evolutionary theory to the study of behavior. It grew out of the integration of classical ethology (the naturalistic study of animal and human behavior), population ecology, and population genetics during the 1960s and early 1970s.

The fundamental breakthrough at the heart of sociobiology was provided by a solution to the problem of ALTRUISM. Ever since DARWIN, it had been recognized that altruistic behavior (such as alarm-calling) whereby an individual incurs a potentially life-threatening cost while others benefit creates an anomaly for Darwinian thinking. Any gene for such behavior would soon be eradicated from the population because its carriers would die prematurely, leaving few descendants, while "cheats" who exploited the behavior of the altruist would survive and leave many descendants. W. D. Hamilton provided the solution to this problem in a pair of seminal papers published in 1964. He realized that the anomaly evaporates when the unit of evolutionary accounting is the gene and not the individual: relatives share a proportion of their genes in common by virtue of the fact that they inherit them from the same common ancestor. A gene for altruism can thus evolve whenever the benefit to the altruist via its relatives is greater than the cost it bears through lost personal reproduction, even if the altruist dies in the process.

This observation is the basis of kin selection theory and provides the single most important theorem in sociobiology, known as Hamilton's rule. This in effect points out that the genetic fitness of a gene (loosely, the effectiveness with which it replicates itself in future generations) is made up of two components: the number of copies transmitted to the next generation through an individual carrier's own reproduction, and the number of copies of the same gene transmitted to the next generation through the additional reproduction achieved by his or her relatives as a direct result of that individual's actions. This combined measure is referred to as inclusive fitness.

The crucial assumption underlying this new perspective is that natural selection favors those behaviors that allow genetic fitness to be maximized (the so-called selfish gene perspective). However, the Darwinian formula for natural selection does not contain within it any explicit reference to DNA or genes (neither of which were known in the mid-nineteenth century). Rather, the modern theory of neo- Darwinisim is built on the integration of Darwin's theory of natural selection with Mendel's theory of inheritance. Because Mendel's theory is concerned with the heritability of characters (or phenotypes) and not genes as such, it follows that anything that can faithfully copy itself is in principle a Darwinian entity and will evolve subject to the laws of natural selection. Learning and the transmission of cultural rules by imitation thus come under the remit of sociobiology as bona fide Darwinian processes.

It is important to appreciate that sociobiology makes no presuppositions about the genetic bases of behavior. The sociobiological perspective is concerned with functional explanations of behavior and centers on the question of whether an organism's behavior (or traits) are designed to maximize inclusive fitness. Although an intrinsically interesting question in itself, the issue of whether the mechanism of inheritance is genetic or learning is irrelevant to the sociobiological approach. Evolutionary theory assumes that organisms are locked into a perpetual scramble for representation in the next generation, but an important distinction thus has to be drawn between the processes involved at the level of the "gene" (the notional unit on which natural selection acts) and the behavioral mechanisms that implement these processes at the level of the individual. One of the central principles of evolutionary biology is that the "selfishness of genes" (the gene's imperative to replicate itself) may be expressed as cooperativeness at the level of the individual.

This important distinction lies at the root of many of the controversies that were generated by the emergence of sociobiology. Many critics assumed, for example, that sociobiology assumes that all behavior is genetically determined. However, such a view would be both biologically unrealistic and would miss the very insight that lies at the heart of Darwinian evolutionary theory. Nonetheless, the adoption of evolutionary ideas in disciplines outside of biology has sometimes resulted in views that approach a form of strict genetic determinism more strongly than is either justified or necessary.

These controversies aside, the extent to which evolutionary thinking revolutionized the understanding of animal behavior during the 1970s justifiably led to its being referred to as the sociobiological revolution. The explanatory power of its theories explained many previously puzzling phenomena, and their predictive power generated many new research programs in both the field and the laboratory. The sociobiological approach has widely been acknowledged as being especially successful in explaining foraging behavior, conflict resolution, mate choice patterns, and parental investment decisions in animals, as well as many aspects of communication and signaling.

The early success of the application of these ideas to the study of animal behavior inevitably raised the possibility of their being applied to human behavior. The early sociobiological discussions of human behavior were based on very limited empirical evidence, and were much criticized for their naivety as a result. However, since the mid-1980s, there has been a dramatic growth in the number of empirical studies. These included studies of both traditional societies, contemporary postindustrial Western societies, and historical societies, with the main focus being on mate choice, reproductive decisions, inheritance patterns, foraging strategies, and cultural evolution mechanisms (see Betzig, Mulder, and Turke 1988; Smith and Winterhalder 1992).

More recently, a second dimension has developed out of human sociobiology that focuses more on the cognitive mechanisms that underpin behavior. Because the sociobiological perspective was concerned exclusively with functional explanations of behavior (the purpose that behavior serves in the life history of the individual organism), little attention was given to the cognitive mechanisms underpinning these behavioral processes. A growing interest in these issues, informed by an evolutionary perspective, now makes it possible to distinguish two subdisciplines, at least in the context of research on humans: evolutionary anthropology (which focuses on the adaptiveness of individuals' behavioral decisions) and EVOLUTIONARY PSYCHOLOGY (which focuses on the cognitive mechanisms involved in the making of such decisions). The two subdisciplines are divided by the issue of whether contemporary human behavior is ever functionally adapted.

Evolutionary psychologists argue that because the cognitive mechanisms that guide behavior evolved during the Pleistocene and have been overtaken by rapid changes in culture and technology, the behavior they generate will commonly be nonadaptive: in effect, we operate with Stone Age minds in a Space Age environment. Instead, evolutionary psychologists typically focus on the design features of human cognition that give rise to universal patterns of behavior that are true of all humans (for some examples, see Barkow, Cosmides, and Tooby 1992). In contrast, evolutionary anthropologists argue that many aspects of behavior are still functionally adaptive, and most of their research is directed to empirical tests of the functional consequences of behavioral decisions. They focus on the adaptive flexibility of behavior at the level of the individual (for examples, see Betzig, Mulder, and Turke 1988; Smith and Winterhalder 1992).

Although it is no doubt true that cognition constrains behavior, it is a purely empirical question as to whether or not our cognitive mechanisms are sufficiently flexible to operate effectively in the modern world. The wealth of studies demonstrating that human and animal behavior is functionally adaptive despite radically changed environments undermines the strong version of the evolutionary psychologist's position, though there must surely be some aspects of behavior that are now maladaptive in this sense.

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-- R. I. M. Dunbar


Barkow, J., L. Cosmides, and J. Tooby, Eds. (1992). The Adapted Mind: Evolutionary Psychology and the Generation of Culture. Oxford: Oxford University Press.

Betzig, L., M. Borgerhof Mulder, and P. Turke, Eds. (1988). Human Reproductive Behaviour. Cambridge: Cambridge University Press.

Buss, D. (1994). The Evolution of Desire. New York: Basic Books.

Daly, M., and M. Wilson. (1983). Sex, Evolution and Behavior. Belmont, CA: Wadsworth.

Daly, M., and M. Wilson. (1988). Homicide. New York: Aldine.

Dawkins, R. (1986). The Selfish Gene. 2nd ed. Oxford: Oxford University Press.

Dawkins, R. (1983). Universal Darwinism. In D. S. Bendall, Ed., Evolution from Molecules to Men. Cambridge: Cambridge University Press, pp. 403-425.

Dawkins, R. (1995). River Out of Eden. London: Weidenfield and Nicolson.

Dunbar, R. I. M., Ed. (1995). Human Reproductive Decisions: Biological and Social Perspectives. Basingstoke: Macmillan.

Hamilton, W. D. (1964). The genetical evolution of social behaviour, 1, 2. Journal of Theoretical Biology 7:1-51.

Hughes, A. (1985). Evolution and Human Kinship. Oxford: Oxford University Press.

Ridley, M. (1993). The Red Queen. Harmondsworth: Penguin.

Smith, E. A., and B. Winterhalder, Eds. (1992). Evolutionary Ecolo gy and Human Behavior. New York: Aldine.

Wright, R. (1995). The Moral Animal. London: Little Brown .