SOCIOBIOLOGY, HUMAN

THE DARWINIAN SETTING

Sociobiology is the term used to describe a relatively recent stage in the continuing development of evolutionary biology. It systematically brings the study of social behavior under the umbrella of the Synthetic Theory (or the Modern Synthesis) that, starting in the 1920s, arose from the marriage of Darwinian theory and Mendelian, or genetic, science (Huxley 1942). The most challenging aspect of the new elaboration concerns a decisive step into human behavior. Sociologists (and social scientists in general) have not responded with enthusiasm; the old anthropocentrism with its extreme stress on culture and socialization (environmentalism) is still dominant. Resistance, however, is slowly breaking down, and one may speak of a human sociobiology taking the form of "evolutionary anthropology," "evolutionary psychology," "evolutionary sociology", and so forth. It can even be stated that human sociobiology may represent the beginning of the long-desired synthesis of the social sciences. At the same time, the introduction of cultural parameters into evolutionary explanation may further enrich the modern synthesis.

The term "sociobiology" harks back to the mid-1940s, and the evolutionary study of behavior began to develop rapidly only in the 1960s. However, its roots can be traced back to Darwin's ([1859] 1958) theory of evolution by natural selection, still the cornerstone of evolutionary science. From today's perspective, Darwin's theory can be conveniently stated as follows:

1. The rate of reproduction in populations, such as species, tends to be faster than the growth of the resources needed to sustain all their members.
2. As a result, populations experience a real or potential scarcity of resources.
3. This scarcity stimulates the "struggle for existence": competition of various kinds both within and between populations.
4. Some individuals in any given population are more succeessful than others in the struggle and thus are more likely to survive long enough to reproduce.
5. This differential reproductive success is in the last analysis the result of "variations" between individuals: genetic differences. That is, some variations are better suited (adapted) than others for the competition.
6. The better adapted these variations are, the more likely they are to be inherited by one's descendants.
7. This generational preservation of favorable variations and the concomitant elimination of unfavorable ones are together referred to as "natural selection."

This theory either contains or fosters the basic elements of the theoretical program of sociobiology. Specifically, (1) it establishes natural selection as the basic mechanism in the evolution of behavior, (2) its stress on competition calls attention to the perennial question regarding the role of altruism and selfishness in social life, (3) its focus on heredity suggests that aspects of human behavior, including culture, may be at least partly the result of natural selection and thus of forces long at work in human evolution, (4) perhaps more important, it guides inquiry toward a systematic theory of human nature. The crucial question of this theory is: In the course of human evolutionary time, what innate behavioral tendencies (predespositions, psychological adaptations, epigenetic rules, etc.) have been forged by natural selection and environmental pressures acting on genetic matter? These adaptations are likely to be implicated to some degree in socialization processes, thus proposing a more complete explanation in social science.

ELEMENTS OF SOCIOBIOLOGICAL THEORY

The modern synthesis stimulated scientific activity in general and, through such disciplines as entomology, primatology, and ethology, paved the way to the evolutionary study of behavior. Then in 1975 a seminal work proclaimed the advent of a "new synthesis" (Wilson 1975). The master stroke of sociobiology is the revival of "the struggle for existence," that is, the behavioral aspect of evolution on which natural selection was clearly based in the work of Darwin. The ultimate consequence of this struggle, or competition for resources, is natural selection: the differential contribution of offspring to future generations. This differential is a rough measure of what Darwin, following the sociologist Herbert Spencer, called "fitness." Accordingly, we are already in a position to state that in the last analysis individuals (or simply organisms) may be productively viewed as being in competetion with one another for reproductive success, or genetic fitness. (Without the behavioral component, the statement would read, classical Darwinian logic: Organisms are the descendants of the more reproductively successful organisms.)

The Maximization Principle. This Darwinian-Mendelian idea is rendered more formally by what is considered the general law or principle of sociobiology. Sometimes referred to as the maximization (or fitness) principle, this law states that, while organisms engage in all sorts of behaviors, in the last analysis they tend to behave in ways that maximize their inclusive fitness, or the chance of conveying their genotype (genetic makeup) to future generations. This is a probability statement: That is, some individuals are more successful than others in the reproductive competition. This idea of variability reflects the logic of natural selection and accommodates many facts that may seem strange or contradictory of evolutionary theory. A case in point is the parental abuse of children. Clearly, if organisms differ in the degree to which they behave adaptively one effective way to show this is for them to differ in the way they treat their children. However, this statement is heuristically a bit "lazy": It stimulates research insufficiently. Like many other laws in science, it would be more useful if it took the form of a contingent proposition. A first approximation in this direction is available and the provisos proposed are "creature comforts," "self-deception," and "autonomization of behavior" (the tendency of means, such as wealth, to become ends in themselves), all of which appear to condition negatively the maximization tendency (Lopreato 1989; for incisive analyses of this argument, see Crippen 1994; Maryanski 1998, pp. 11–16; Maryanski and Turner 1998, pp. 128–131).

The use of the adjective "inclusive" is intended to underscore the fact, better understood in the post-Darwinian period (Hamilton 1964), that the fitness of organisms is measured in terms of their relatedness both to their offspring and to other members of their genetic kin, whom they typically favor in many fundamental ways over nonkin. Hence, family life issues are central foci of sociobiology. Also, the maximization principle does not fit neatly into the mold of individual experiences. Human beings are not overtly obsessed with the enhancement of their fitness, and some, as was noted above, actually behave maladaptively. It is necessary to keep in mind, therefore, that the principle does not assume consciousness of the fitness consequences of behavior.

The fitness principle performs various functions. The crucial one is to logically structure established discoveries and thus stimulate cumulative, systematic knowledge. Central in this undertaking is the discovery of the mental rules that may be said to constitute human nature. Are people, for example, constituted to facilitate the persistent prejudices and ethnic affiliations that periodically flare up in bloody conflicts across the globe? Surely, people grow up with such prejudices and absorb them, but why is this learning universal? Is it possible that it is an effect of evolutionary forces? To learn any given behavior, one must have a capacity for it in the brain. Try as humans might, they never can be socialized to behave like foxes, or like any other animal. Aristotle was correct in his metaphor of the oak acorn: If an acorn becomes anything, it can only become an oak, never, say, a fig tree.

The Law of Altruism. As fitness theory develops, the principle surrounds itself with auxiliary statements of theory that facilitate the quest for a theory of human nature. In what follows, this article touches on a few of these. Let us start by noting that central to sociobiological reasoning is the metaphor of "the selfish gene" (Dawkins 1976), which recalls the so-called Hobbesian question of order: For whose benefit does the individual behave? Selfishness is such a prevalent concept in evolutionary science that according to Wilson (1975, p. 3), the question of its opposite, what the sociologist Auguste Comte termed "altruism," constitutes "the central theoretical problem of sociobiology." Acts that benefit others are commonly observed in all behavioral disciplines. How to explain them? The social and moral disciplines have been of little help, largely because of the ambiguity of their concepts. What seems altruistic to scholar X is viewed as selfish by colleague Y.

Sociobiologists have taken a major step toward the solution of this problem. Countless observations coupled with the logic of the fitness principle have led to the position that altruism strictly viewed refers to genetically "self-destructive behavior performed for the benefit of others" (Wilson 1975, p. 578). In short, genuine altruism reduces the benefactor's fitness; hence, if it arises in a given population, natural selection may be expected to wipe it out fairly quickly. If, for example, Mary is driven by her genes to do good for John at the expense of her own reproductive interest (e.g., cohabit with him and then be abandoned childless at an age when her chances of marriage and/or reproduction are greatly reduced), her altruistic genes will not be represented in the next generation (unless they are conveyed by her blood kin). What is it, then, that people call altruism? Typically, it is either favoritism toward kin (nepotistic favoritism) or favoritism accompanied by the expectation of reciprocation (reciprocal altruism). Both types benefit the "altruist," sometimes with interest. Evolutionists' venture into the topic of altruism has produced rich harvests, particularly the discovery of kin selection and inclusive fitness (Hamilton 1964) and the theory of reciprocal altruism (Trivers 1971), which together yield the law of altruism.

Kin selection and inclusive fitness are dramatically illustrated by the study of eusocial insects, such as ants. Approximately three-quarters of these animals are female ("workers"), and very few reproduce. It would be a mistake, however, to consider them genuine altruists. Workers are so named because they are very diligent in catering to the needs of the queen (typically their reproductive mother) and her prodigious brood. Furthermore, given their peculiar reproductive system (haplodiploidy, whereby females have both parents while males, hatched from unfertilized eggs, have only a mother), workers are more closely related to the future generations than are their counterparts in diploid species such as mammals. As a result, failure to reproduce results in little or no loss in fitness. In short, eusocial insects have evolved according to kin selection and inclusive fitness. Indeed, this strategy is widespread among social animals. In humans, this fact is underscored by last wills and testaments, according to which people rarely bequeath their (fitness-enhancing) resources to anyone except blood kin (Clignet 1992).

Kin Selection and Ethnic Conflict. The familism inherent in kin selection has numerous expressions. One is related to the widespread phenomenon of ethnic identification and the recurrent cases of ethnic violence that often take everyone but the participants by surprise. More than eighty years ago, Pareto applied the logic of kin selection to explain the formation of persistent groups such as ethnic groups. They are "natural formations," he argued (1916, section 1022), "growing up about a nucleus which is generally the family, with appendages of one sort or another, and the permanence of such groups in time engenders or strengthens certain sentiments that, in their turn, render the groups more compact, more stable, better able to endure." This evolutionary perspective on ethnicity and ethnocentrism had been foreshadowed by Sumner (1906) and was subsequently approximated by several sociologists (e.g., Park and Burgess 1921; Gordon 1964). More recently, van den Berghe (1981) produced a thoroughly evolutionary theory of ethnicity and ethnic conflict (see also Lopreato and Crippen 1999, chap. 9).

Sociologists continue to debate the causes of ethnic phenomena, typically focusing on cultural factors, such as differences in language or religion, that are specific to given times and places. Are such factors relevant? Very probably, but ethnic phenomena are persistent and universal; across the globe there are numberless mixtures of peoples who have an awfully hard time living together in peace. Any universal phenomenon requires first and foremost a universal explanation.

In brief, during nearly all of human evolutionary history people lived in small bands of about twenty-five to fifty individuals, often surrounded by neighbors who coveted their resources. Warfare or the threat of it was frequent. Benedict (1934, pp. 7–8) described "primitive man": "From the beginning he was a provincial who raised the barriers high. Whether it was a question of choosing a wife or taking a head, the first and important distinction was between his own group and those beyond the pale. His own group, and all its ways of behaving, was unique." Intense internal solidarity was a precondition of survival. To practice it was also to practice kin selection and kin favoritism. Since the modern human brain evolved in such circumstances, it can be concluded that the tendency to identify with one's own "clan"—to distinguish between "us" and "them"—is alive and well in human society. Ethnicity is an extension of the family. Nepotistic favoritism is wired in the brain, and at the ultimate or general level it and the kin selection to which it is inextricably associated are the cause of the persistence of ethnic identification and recurrent ethnic conflict. "Who am I?" "Who are mine?" These are enduring whispers in the human psyche.

Of course, it is difficult to answer such questions in the megasociety, and that is one reason why most of the time people live in a reasonably peaceful relationship with their neighbors. Still, people are attentive to markers of "weness" such as a common name, common historical experiences, distinctive cuisine and artistic expressions, and often a common language, in historical time if not now (van den Berghe 1981).

Reciprocal altruism. Reciprocal altruism refers to the fact that if and when people engage in actions that benefit others, they do so with the expectation, conscious or not, that the others will repay, especially if they are not related. This is the object of a much-tested and growing theory first stated by Trivers (1971). According to the basics of this theory, the evolution of reciprocal altruism was facilitated by three broad conditions: (1) repeated situations in which the value of altruism to beneficiaries was, in terms of fitness, greater than the cost incurred by the benefactors, (2) membership in a small group featuring little or no migration, thus enhancing the chances of reciprocity, (3) fairly equal ability between pairs of individuals to engage in mutual help. Trivers proceeds to argue that a system of reciprocal altruism is subject to "cheating": Some individuals do not reciprocate the benefits they receive. Indeed, an underlying assumption of Trivers's theory is that givers are motivated to receive more than they give. Accordingly, as reciprocal altruism was evolving, another set of adaptations, what Trivers terms a "psychological system," was arising fairly in step with it; their function was to regulate cheating. They include emotions such as friendship, sympathy, trust, suspicion, and moralistic aggression, along with hypocrisy and feelings of guilt.

Combining the logic of kin selection and reciprocal altruism, it is possible to state a law of altruism as follows: In keeping with the fitness principle, social oganisms have evolved to favor others (1) in direct proportion to their degree of genetic relatedness to them and (2) to the extent that the benefit they derive from doing good to others is, in terms of fitness, equal to or greater than the cost of their altruism.

The law is relevant to various human phenomena, and casts light on a number of puzzles. For instance, social scientists have noted that the exchange of gifts is a universal institution in human society (Mauss [1925] 1954). Moreover, a version of this tendency termed "potlatch" is in varying degrees "a universal mode of culture" (Lévi-Strauss [1949] 1969). In an extreme form of potlatch practiced by the "Indians" of Vancouver and Alaska, one gives with a view to crushing another and thus gaining "privileges, titles, rank, authority, and prestige" (Lévi-Strauss [1949] 1969, chap. 5). Specifically, gifts are given to a competitor with the shared understanding that the recipient will reciprocate with interest after a reasonable interval. When such an obligation cannot be met, the recipient loses status, titles, and so forth. Social theorists have been eager to downplay the individual's selfish undercurrent and the social conflict it engenders. The law of altruism conversely predicts selfishness, competition, and precariousness of status in one's group.

Nevertheless, the extreme stress on selfishness cannot go unchallenged for the human species. The only known attempt of this sort avoids the genetic trap (altruists are by definition "selected out"). Using a biocultural perspective at the core of which is the evolution of the idea of the soul and self-deception, it concludes that behaviors intended to save the soul mimic fitness-enhancing behaviors (Lopreato 1984, pp. 207–235). Catholic nuns and Buddhist monks, for example, practice celibacy and other forms of ascetc behavior in view of immortal ends. Typically, they contribute little or nothing to the fitness-enhancing resources of their blood relatives. Yet their type manages somehow to "reproduce" itself. Genuine or "ascetic" altruism may be rare in human society, but it is a cultural fact.

The Law of Anisogamy. Human psychological adaptations may be divided into two major types. One is specieswide, referring to innate tendencies that in varying degrees cut across gender. Examples include tendencies toward kin favoritism, ethnic identification, reciprocal altruism, and cheating. The other major class accounts for the fact that throughout human society there have been some remarkable differences, as well as similarities, along sex lines (Trivers 1972; Kimura 1992; Lopreato and Crippen 1999). The differences are suggested by a basic diversity in physioanatomy. Anisogamy, the name given to it, refers to the difference in size and structure between male and female sex cells (gametes). Male gametes (sperm) are minuscule and contribute only genes to reproduction. They are produced in huge quantities almost continuously after the onset of sexual maturity. The reproductive potential of males is therefore huge, and some men have fathered thousands of children (Betzig 1986). By contrast, female gametes are much larger, are nutritious, and are produced in utero once in a lifetime. Then, beginning at menarche, they are released, typically one at a time, about once a month, so that on average women produce some 300 to 400 mature eggs in a lifetime, only a very small number of which are likely to result in offspring. Women are constitued to bear the cost of pregnancy, nursing, and much of the protection and guardianship, at least during the offspring's tender years. In short, each child represents a huge reproductive investment for the typical woman.

By contrast, males make a very small investment. They do not get pregnant or suffer nausea; nor do they risk their life at the birth of a child and for months or years afterward. If we consider such other facts as abandonment, divorce, and the refusal or failure to provide child support, the level of paternal investment is on average truly puny. There is no intention here to condemn men or glorify women. It is a matter of trying to grasp certain facts in order to understand certain others. Males and females have evolved under the pressure of significantly different, though partly complementary, reproductive strategies, and much of their behavior is an effect of this fact. It is now time to state what was earlier termed the law of anisogamy (Lopreato 1992, p. 1998): The two sexes are endowed with differing reproductive strategies, and their behaviors reflect that difference in direct proportion to their relevance to it. The closer one gets to the fundamental activities of life (sexual behavior, family life, and among endless others the conditions that recall the division of labor in the clan, the type of society in which the human species spent 99.5 percent of its history), the more likely one is to observe the effects of anisogamy. The basic implications of anisogamy have been drawn by Trivers (1972) in a seminal paper on "relative parental investment."

Differential Parental Investment and Sexual Selection. The law of anisogamy contains a number of corollaries. The two major ones noted briefly here are very closely related. Differential parental investment (DPI) states in effect that females make both a greater initial parental investment and greater subsequent parental investments than do males, so that their behavior is more finely adjusted to the well-being and reproductive success of the offspring. Supporting facts are legion. They are epitomized by the following widely noted findings, among others: On average females are more cautious than males in their sexual activity, and they tend to prefer as mates men who are in fact, or show promise of becoming, relatively rich in the resources needed to raise healthy and reproductively viable offspring. Mating has always been far riskier for women, and this fact is deeply rooted in the brain. As a consequence, it tends to express itself even in times and places where mating need not have reproductive consequences. For millions of years, and even today in much of the world, an unwanted pregnancy or a pregnancy with a partner who will contribute little or nothing to the well-being of the offspring may consume a large portion of a woman's reproductive potential. In summary, women go for quality; men, for the allure of quantity.

A study of 10,047 individuals living in various countries on six continents strongly suggests that culture has a notable influence on mate preferences and that the two sexes agree on some of the basic requirements of a good mate, such as honesty and dependability. However, the findings also reveal some marked universal differences that are predictable from the law of anisogamy. For instance, females are significantly more likely than males to emphasize ambition and industriousness. Conversely, males more than females prefer mates who are physically attractive, younger than themselves, and at the peak of their reproductive value even if they are of lower socioeconomic status (Buss 1989).

The sexual selection (SS) corollary may be stated in Trivers's (1972, p. 140) words as follows: "Individuals of the sex investing less will compete among themselves to breed with members of the sex investing more, since an individual of the former can increase its reproductive success by investing successfully in the offspring of several members of the limiting sex."

The idea of sexual selection is a remarkable example of great ideas that emerge out of creative confusion. Darwin understood that in the final analysis the measure of survival is reproductive success. Nevertheless, he tended to focus on survival as longevity. As a result, certain observations, both behavioral and physical, confronted him with a special challenge. Why the great horns, the displays, the mimicry, the special weapons, "the instrumental music," or, among other male characteristics, the huge tail of the peacock? Such unusual features tend to attract predators and thus reduce longevity. Darwin (1859, but especially 1871) concluded that if such "secondary sexual characters" enhance the bearers' ability to reproduce, they are likely to be favored by natural selection even if they act negatively on longevity. However, because such characters were conspicuous in sexual competition, they suggested to him the label "sexual selection." There is some debate over the meaning of this term (see Mayr 1972 for a review), but it is safe to say that it refers not to a type of selection but instead to a major cause of natural selection. "After all," as Dobzhansky et al. (1977, p. 118) noted, "Darwinian fitness is reproductive fitness," whatever the cause. Sexual selection, or competition for mates, refers most explicitly to the struggle for genetic survival. It further suggests that much animal behavior and appearance are adapted not so much to the problem of daily survival as to the job of securing adequate mates.

Viewed as competition, sexual selection has become a valuable tool of research, especially in view of certain distinctions suggested by Darwin himself. In current language there are two major types of sexual selection. One, often termed "intrasexual selection," subsumes a female-female competition and a male-male one. The other refers to a form of male-male competition, too (the competition "to charm the females"), but Darwin viewed it as an effect of the females' response to "charm." Accordingly, it has come to be known as female choice (or "intersexual selection"). It is evident that differential parental investment and sexual selection are closely linked properties of anisogamy. In fact, one may combine the logic of DPI and SS to state what may be termed the DPI-SS corollary as follows: Given anisogamy, females have been selected to engage in choosy behavior, while males have been selected to specialize in agonistic behavior.

Female choosiness in human beings takes many forms. This article has mentioned the tendency to prefer resource-rich mates. As a group, even in a highly developed society like the United States, women pay less attention to looks, have and claim to want fewer sexual partners, are less likely to have their first sexual experience with a stranger, are more likely to expect a commitment before engaging in sex, and among many other differences, are less likely to cheat on their mates, whether husbands, cohabitors, or boyfriends (Laumann et al. 1994).

Competitiveness, too, takes many forms. One is reflected in the ancient and still fairly common practice of polygyny, especially if one considers the greater tendency of divorced men to remarry and have further children (Betzig 1986; Lenski and Lenski 1987). Another form is expressed in violent behavior. Killing, for example, is throughout the world a largely male behavior and is concentrated among young men during the peak years of their reproductive life. Prominent among the motives for homicide are sexual jealousy and rivalry as wall as dominance contests in various contexts (Daly and Wilson 1988). Death by trauma (murder and accidents) accounts for a relatively high percentage of male mortality and part of the lower life expectancy of men (Verbrugge 1989). Of course, there are many other forms of competitiveness, and women are not immune to the tendency to practice them.

Of Sex Roles. Sociological practice is almost entirely environmentalist and often clashes with an evolutionary perspective. For example, according to "feminist" authors, especially so-called gender feminists, men and women are born with identical potentials. The idea that, given anisogamy, the brain has been neuroendocrinally gendered (Kimura 1992) is extraneous if not altogether offensive to them. They argue conversely that society is ruled by a system of patriarchy, and socialization thus proceeds to produce differences that are detrimental to women. Girls are socialized to be passive and subordinate, while boys are trained to strive for success and dominance (Lerner 1986, p. 29). In short, so-called sex roles are the effect of culturally prescribed discrimination and must be explained in terms of cultural causes only. Some writers go so far as to argue that physiology is irrelevant or that "human physiology is socially constructed and gendered" (Lorber 1994, p. 46; emphasis added).

Sociobiologists do not deny that once an arrangement such as patriarchy is in place, the channels of socialization tend to develop in view of its mandates. However, science does not merely assert facts; it seeks to explain them. As Hrdy (1997, pp. 7–8; italics in the original) notes, "an evolutionary perspective pushes the search for patriarchy's origins back . . . by millions of years by asking an additional question: Why should males seek to control females?" That is, why patriarchy in the first place? Accordingly, it less superficially identifies sexual selection "rather than male desire for power as the engine driving the system" of patriarchy.

To understand patriarchal phenomena and have more than a wishful chance of bringing effective cultural forces to bear on them, one must begin by answering Hrdy's question. In the process, a very unpleasant irony will be uncovered. The dynamics that produced patriarchy include female complicity with domineering males. Male dominance has been achieved at least in part because of female preference (female choice) for dominant males. Indeed, males dominate females by dominating other males with female help. Thus, the pickle that many people find so distasteful "turns out to have been seasoned with only a sprinkle of culture at best, although once culture arose it made it even more tartish. It is also true that our female ancestors had a hand in the preparation" (Lopreato and Crippen 1999). Moreover, women throughout the world continue to support patriarchy through their persistent tendency to favor dominant males.

CONCLUSION

In order to advance, would-be sciences need to discover the value of a number of time-tested techniques. These techniques include especially the use of remote concepts and logical ways to operationalize them, the nomothetic derivation and testing of hypotheses, and the logical structuring of the hypotheses in a body of systematic, cumulative knowledge that facilitates further research and discovery. The history of science strongly suggests that to accomplish even these minimal feats, it is necessary to either discover one general principle or to borrow it in full or modified form from a cognate and more advanced science. At the start of the third millennium there is still no general principle in sociology, general in the sense that it would contain the logic for a large number of derivative statements linking discovery and explanation across the institutional framework. The fitness principle and the theoretical tools surrounding it constitute an invitation from sociology's most proximate natural science to embrace the fact that the human brain represents a tenacious link to a past that in part is still present. The potential payoff is likely to be far greater than even the most sanguine evolutionists can imagine. It may suffice to consider that just as Newtonian laws eliminated the old prejudice of geocentrism, thus freeing the mind to behold previously inconceivable wonders of nature, sociobiology offers a human perspective from a distance, thus freeing the mind from the still-oppressive assumptions ofanthropocentrism and temporecentrism, benighting corollaries of geocentrism.

According to many critics of sociobiology, since certain behaviors are "natural," they are not subject to cultural intervention. This is an error that sociobiologists do not commit. Because they are evolutionists, their theorizing is subject to a systemic perspective: "Phenotype" (any feature of anatomy, physiology, or behavior) is a result of the interaction between genotype and environment, including culture. It is essential to have knowledge of both. To change the world, as many scholars are inclined to do, with knowledge (always imperfect) of one to the exclusion of the other is not only obscurantism; it is poor, perhaps dangerous, engineering as well.

references

Benedict, R. 1934 Patterns of Culture. Boston: Houghton Mifflin.

Betzig, L. L. 1986 Despotism and Differential Reproduction: A Darwinian View of History. New York: Aldine.

Buss, D. M. 1989 "Sex Differences in Human Mate Preferences: Evolutionary Hypotheses Tested in 37 Cultures." Behavioral and Brain Sciences 12:1–49.

Clignet, R. 1992 Death, Deeds, and Descendants. New York: Aldine.

Crippen, T. 1994 "Toward a Neo-Darwinian Sociology: Its Nomological Principles and Some Illustrative Applications." Sociological Perspectives 37:309–335.

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

Darwin, C. (1859) 1958 The Origin of Species. New York: Mentor.

—— 1871 The Descent of Man and Selection in Relation to Sex. New York: Appleton.

Dawkins, R. 1976 The Selfish Gene. Oxford: Oxford University Press.

Dobzhansky, T., F. J. Ayala, G. L. Stebbins, and J. W. Valentine 1977 Evolution. San Francisco: Freeman.

Gordon, M. M. 1964 Assimilation in American Life. New York: Oxford University Press.

Hamilton, W. D. 1964 "The Genetical Theory of Social Behaviour: I and II." Journal of Theoretical Biology 7:1–52.

Hrdy, S. B. 1997 "Raising Darwin's Consciousness: Female Sexuality and the Prehominid Origin of Patriarchy." Human Nature 8:1–49.

Huxley, J. 1942 Evolution: The Modern Synthesis. New York: Harper.

Kimura, D. 1992 "Sex Differences in the Brain." Scientific American 268:119–125.

Laumann, E., R. Michael, S. Michaels, and J. Gagnon 1994 The Social Organization of Sexuality. Chicago: University of Chicago Press.

Lenski, G., and J. Lenski 1987 Human Societies. New York: McGraw-Hill.

Lerner, G. 1986 The Creation of Patriarchy. Oxford: Oxford University Press.

Levi-Stauss, C. (1949) 1969 The Elementary Structures of Kinship. Boston: Beacon.

Lopreato, J. 1984 Human Nature and Biocultural Evolution. London: Unwin Hyman.

—— 1989 "The Maximization Principle: A Cause in Search of Conditions." In R. W. Bell and N. J. Bell, eds., Sociobiology and the Social Sciences. Lubbock: Texas Tech University Press.

—— 1992 "Sociobiology." In E. F. Borgatta, ed., Encyclopedia of Sociology. New York: Macmillan.

——, and T. Crippen 1999 Crisis in Sociology: The Need for Darwin. Rutgers, N.J.: Transaction.

Lorber, J. 1994 The Paradoxes of Gender. New Haven, Conn.: Yale University Press.

Mauss, M. (1925) 1954 The Gift. London: Cohen and West.

Maryanski, A. R. 1998 "Evolutionary Sociology." Advances in Human Ecology 7:1–56.

——, and J. H. Turner 1998 "New Evolutionary Theories." In J. H. Turner, ed., The Structure of Sociological Theory, 6th ed. New York: Wadsworth.

Mayr, E. 1972 "Sectual Selection and Natural Selection." In B. G. Campbell, ed., Sexual Selection and the Descent of Man. Chicago: Aldine.

Pareto, V. (1916) 1963 A Treatise on General Sociology. New York: Dover.

Park, R. E., and E.W. Burgess 1921 Introduction to the Science of Sociology. Chicago: University of Chicago Press.

Sumner, W. G. 1906 Folkways. New York: Ginn.

Trivers, R. L. 1971 "The Evolution of Reciprocal Altruism." Quarterly Review of Biology 46:35–47.

—— 1972 "Parental Investment and Sexual Selection." In B. H. Campbell, ed., Sexual Selection and the Descent of Man, 1871–1971. Chicago: Aldine.

van den Berghe, P. L. 1981 The Ethnic Phenomenon. New York: Elsevier.

Verbrugge, L. M. 1989 "The Twain Meet: Empirical Explanations of Sex Differences in Health and Mortality." Journal of Health and Social Behavior 30:282–304.

Wilson, E. O. 1975 Sociobiology: The New Synthesis. Cambridge, Mass.: Harvard University Press.

Joseph Lopreato