Sociobiology

Sociobiology Theory

Sociobiology is the systematic study of how natural selection shapes the biological basis of all social behavior (Wilson, 1975).

Patterns of human social behavior can be explained by biological imperatives such as the drive to spread genetic inheritance as widely as possible.

Sociobiology distinguishes itself from evolutionary psychology, which stresses mental mechanisms more than genes as the evolutionary determinant of adaptiveness.

According to sociobiology, whole society traits are the outcomes of Darwinian evolution, and human as well as animal sociality depends on how genes and culture have co-evolved (Lumsden, 2011).

This claim proved highly contested.

The early 1970s saw a significant theory of both theoretical and empirical approaches to the study of animal social behavior from an evolutionary perspective.

Scientists hoped to understand social behavior in the same way that they understood morphological traits such as skin tone and eye color.

However, others saw the extension of an evolutionary perspective to human behavior as both politically dangerous and scientifically unsound (Segerstrale, 2015). The debate did not stay academic for long.

Wilson was, by training, an entomologist who spent his career studying ants and other social insects. Twenty-six of the book’s twenty-seven chapters covered non-human animals and were largely welcomed as a landmark synthesis.

The controversy came almost entirely from the final chapter. There, Wilson extended the same logic to humans, arguing that sex roles, aggression, and even moral belief could have a biological basis.

The reaction escalated quickly, and two of Wilson’s own Harvard colleagues led the charge:

• 1975: Gould, Lewontin, and other Boston-area academics published an open letter warning that a genetic account of inequality can make social reform look futile.
• 1977: Time magazine put sociobiology’s claims about human nature on its cover, carrying the debate to a mass audience.
• 1978: At a science conference, demonstrators interrupted a talk by Wilson and poured a pitcher of water over his head.

Gould and Lewontin’s objection was political as well as scientific. They were not calling sociobiology equivalent to the discredited doctrine of social Darwinism. Instead, they warned that an unqualified genetic story about inequality can serve the same purpose regardless of the science behind it.

Their approach was methodological, not political.

Sociobiologists assume that social phenomena can be explained by testing hypotheses, the same way a biologist tests a hypothesis about any other trait. Mating preferences, offspring sex ratios, warning calls, parental care, gregariousness, and territorial defense are all treated as data to explain, not just describe.

Sociobiologists are also selectionists: they assume a trait became common because ancestors who carried it were fitter.

George C. Williams pioneered this framing. Scientists began to see organisms as “evolved reproductive strategists.” An organism’s traits, on this view, are tactics for reproductive competition against others of its own kind. The idea applies equally to animals and to non-conscious organisms such as plants.

Inclusive Fitness

One idea that had a significant impact on sociobiology’s early history was William Hamilton’s concept of inclusive fitness or kin selection (1964).

Hamilton proposed that selection will favor any phenotype, or visible trait, that appears to be reflective of the organism’s own genes, regardless of whether these genes are in direct descendants or other relatives.

For instance, the brood care and colony maintenance of sterile worker ants can be selected for favorable if these acts promote the reproduction of a queen who is closely related to the workers.

According to Hamilton, selection maximizes the reproduction of the alleles of all those to whom the organism is related, not just his direct descendants. As a consequence, organisms are nepotistic (Alexander, 1979).

This logic rests on the coefficient of relatedness (r): the probability that a gene in one individual is also carried by a relative through shared ancestry. Full siblings share about half their genes on average.

Helping a relative is therefore a partial substitute for reproducing directly, since it still passes on a share of an individual’s genes.

Ants, bees, and wasps make the logic vivid. Their genetic system, haplodiploidy, means unfertilized eggs become males and fertilized eggs become females.

One consequence is striking: full sisters in these colonies share 0.75 of their genes with each other, more than the 0.5 they would share with their own offspring.

Hamilton (1964) argued this asymmetry gives sterile worker females a genetic reason to raise sisters instead of reproducing themselves. Trivers and Hare (1976) put this to the test.

Later research has qualified the picture. The 3:1 ratio is not universal, and multiple mating by the queen can shift the theoretical optimum. Even so, the study remains a landmark case of a theory generating, rather than merely explaining, a specific prediction.

In his last chapter, Wilson made a bold claim. Human behaviors such as sex roles, aggression, altruism, and even moral and religious belief, he argued, could have a biological basis (Wilson, 1975).

To support this argument, Wilson drew parallels to the behavior of other primates and invoked existing research on selected traits from human behavioral genetics and twin studies.

Critical academics read this very differently. To them, it supported a biologically deterministic view: if social inequality was “in our genes,” social reform would be futile (Segerstrale, 2015).

The criticism of sociobiology soon escalated to a condemnatory letter signed by a number of Boston-area academics and an avoidance of researchers using this term to describe their work.

The pushback did not end there. Robert Trivers built on this concept with a trio of influential papers. His theory of reciprocal altruism (Trivers, 1971) showed that helping unrelated individuals can evolve if the favor is later repaid, converting a short-term cost into a long-term gain.

His later papers on parental investment and parent-offspring conflict (Trivers, 1972) explained why the sexes so often differ in mating strategy.

The “Problem of Altruism”

One central concern of Sociobiology is the so-called “problem of altruism.”

The problem of altruism asks the question of how prosocial behavior, such as altruism, could have evolved as a restraint in aggressive conflict or in facilitating active cooperation.

Here, sociobiologists define altruism as actions whose average consequence is a reduction in the actor’s reproductive success and a direct increase in the reproductive success of someone else (Wright, 2015).

Unlike the definition of altruism used in everyday language, this definition treats the intent to help others as irrelevant.

On first look at Darwin’s theory of evolution, it would appear that selection would always penalize action that is altruistic; yet, many animals perform altruistic behaviors, such as helping to raise the young of others or taking some energetic or predatory risk to warn others of danger.

The most frequently cited answer to the problem of altruism is Hamilton’s inclusive fitness theory (Wright, 2015).

Hamilton’s inclusive fitness theory states that if the person who benefits from an altruistic act is related to the actor, and if that relative’s gain is large in comparison to the actor’s sacrifice, then the effect on the probability that the actor’s genes will be passed down is positive and altruism can increase in relative frequency.

Hamilton specifically proposed the formula, often called “Hamilton’s rule,” that an altruistic tendency will increase in prevalence under selection if r * b > c, where c is the cost to expected direct fitness that the actor must incur, b is the benefit to direct fitness by the beneficiary of the act, and r is the coefficient of relatedness between the actor and the beneficiary; the extent to which the actor and beneficiary have identical genes (Wright, 2015).

A large amount of sociobiological research focuses on testing whether altruistic behavior can be understood according to Hamilton’s rule.

Simply put: help when kinship makes it worth it.

Usually, supportive evidence shows that animals behave differently in correspondence to their relatedness to their interactants or neighbors.

For example, colonial ground squirrels and prairie dogs decide to call out warnings about predators depending on the caller’s degree of relatedness to the others around them.

In a similar sense, adult animals tend to only care for their own young, and those who help care for others’ young tend to discriminate by how related the young is to themselves (Daly and Wilson, 1988; Griffin and West, 2003).

Other research has focused on how animals can recognize kin when they behave nepotistically (Krupp et al., 2011).

In some cases, this discrimination is based on genotypical factors such as odor, while in others, there is merely a pattern of behavior that persists until they are more likely to move away from kin.

For example, a bird may behave cooperatively until they emigrate away from its colony after reaching maturity, a point where they are substantially less likely to encounter those they are highly related to (Wright, 2015).

Those who work in theoretical sociobiology have also tried to formulate solutions to the problem of altruism unrelated to relatedness. Many of these theorists use game theory models.

Animals, according to these models, are in a constant state of exchange, where favors are returned for ones promised in the future.

Robert Trivers’s theory of reciprocal altruism found one of its clearest field tests in vampire bats.

The study became a textbook demonstration that reciprocal altruism happens in nature, though vampire bats’ sharp starvation risk and stable roost membership may make them an unusually favorable case.

Nonetheless, despite attempts to dismantle Hamilton’s theory, it remains fundamental to theories of social evolution (Gardner et al., 2011; Queller, 2011; Wright, 2015).

Sexual Selection and Sexual Conflict

Sociobiological questions around sexual selection revolve around topics such as why organisms reproduce with two parents rather than by themselves and how and why males and females differ in species where there are multiple distinct sexes.

Darwin proposed sexual selection in 1859, elaborated further in 1871. It explains differential mating success across a species.

Darwin contrasted this with natural selection, which is an explanation for why some animals can mate more readily than others due to their success in dealing with survival factors such as finding food and avoiding predators.

The main point of differentiation between sexual selection and natural selection is that sexual selection can favor the evolution of traits, such as a peacock’s vibrant tail, that would put them at a disadvantage in natural selection (by, say, increasing their risk of predation) (Wright, 2015).

Prior to sociobiology, the idea of sexual selection received little attention in academia.

However, Williams (1966) and Trivers (1972) resurrected the concept as a focus of sociobiology by proposing that the extent that sexual selection happens differently in males and females, producing sex differences in anatomy, physiology, psychology, and behavior, was determined by the extent to which the reproductive efforts of one sex were a limiting resource.

The less invested sex competes for the opportunity to mate with the sex that makes the greater reproductive effort, such as caring for offspring (Wright, 2015).

This is parental investment theory. The sex that invests less in each act of reproduction becomes a limiting resource that the higher-investing sex must compete for.

The finding became the seed for Trivers’s theory above. But it has faced serious later scrutiny. Bateman’s method of inferring mate number from marker genetics is now understood to carry a statistical bias. Modern attempts to repeat his procedure have not always reproduced his original pattern.

Sexual selection can cut both ways. This is sexual conflict: a trait that helps one sex can actively harm the other. Chapman et al. (1995) found that male fruit flies’ seminal fluid shortens female lifespan regardless of whether sperm is received.

“Selfish Genes” and Intragenomic Conflict

The fact that selection can act differently on different parts of the genome is a major area of contemporary research. The Y chromosome offers a clear case.

In species where the Y chromosome passes only from father to son, such as fruit flies and humans, a mutation there can spread even when it reduces host fitness. It simply biases offspring toward male chromosomes.

The reverse happens with mitochondrial DNA, which passes only from mother to daughter. There, a mutation can spread by favoring female offspring, even at a cost to overall sexual fitness.

Intragenomic conflict is the name for this: the simultaneous selection of genetic elements working against each other (Wright, 2015).

Recently, scientists have discovered “genomic imprinting,” which is a process where some genes can be activated differently depending on whether they were inherited from one’s mother or father.

This discovery has expanded scientists’ knowledge of potential battlegrounds for intragenomic conflict. Genes of paternal origin, for example, can be selected to produce fetal and infant traits that reduce the odds the mother reproduces again soon (Haig, 2002).

One paternal gene may make an infant cry often. This directs the mother’s efforts away from finding a new mate and toward caring for her current child (Wright, 2015).

Daly (2015) disagrees with a simple picture. In that picture, organisms are strategists purely maximizing their own “inclusive fitness.” Selection can also favor genes that replicate themselves at the expense of the organism’s own ability to reproduce.

Nonetheless, the individual-level focus of sociobiological research persists (Alcock, 2001; Wright, 2015).

Examples

Emotions

Sociobiology brought a new perspective to research on the evolution of emotion in the 1970s and 1980s. The focus shifted from basic emotions to the emotions involved in social interaction (Griffiths, 2001).

Several sociobiologists have argued that “moral emotions,” such as trust, loyalty, guilt, and shame, evolved as a way to mediate social interactions (Weinrich, 1980). They call these evolutionarily stable strategies.

Robert A. Frank proposed that these emotions solve “commitment problems.” A commitment problem arises when the winning strategy requires binding yourself to act against your own interest (Frank, 1988).

Rage and vengefulness, on this view, evolved to let organisms credibly threaten self-destructive aggression, deterring more powerful rivals. Love and guilt evolved for the opposite case: engaging in altruism even when the partner could fail to reciprocate (Griffiths and Gray, 2001).

Altruism in Honey Bees

In insects, the study of social breeding systems has often focused on genes. But gene lists alone cannot show how a trait is actually related to a gene.

Faragalla, Chernyshova, Gallo, and Thompson (2018) tried something new.

They built a “gene network” that reveals connections between genes and behavioral traits in honey bees, connections a simple gene list cannot show. The researchers found that rates of worker sterility could be modeled by these gene networks (Faragalla et al., 2018).

Critical Evaluation

Sociobiology’s boldest human claims made it famous, but its strongest scientific ground lies elsewhere: precise, testable predictions confirmed in non-human animals.

Predictive Successes in Non-Human Biology

The 3:1 female-biased investment ratio in ants (see Inclusive Fitness above) is often held up as one of the most striking predictions in evolutionary biology. It was derived mathematically before anyone collected the data.

A parallel case comes from Trivers and Willard (1973). They proposed that parents in good condition should invest more in sons, since a low-condition son risks failing to reproduce at all.

Parents in poor condition, by contrast, should favor daughters, whose reproductive payoff is more reliable. This pattern has since been confirmed across a wide range of mammal species.

Sherman (1977) found a similar signature in Belding’s ground squirrels. Females, who live near their relatives for life, give predator alarm calls far more often than males, who disperse and have few relatives nearby. The calls track relatedness, not just self-interest.

The Naturalistic Fallacy and Reductionism

Sociobiology’s human-behavior claims ran into a much older logical trap: the naturalistic fallacy. A trait having evolved does not make it good, inevitable, or beyond the reach of policy.

Wilson’s suggestion that inequality might be “in our genes” was widely read as an argument against social reform, whether or not he intended it that way.

A related objection is reductionism. Explaining institutions as complex as marriage law or criminal codes as simple gene-level optimization can flatten a social phenomenon onto a biological substrate too readily.

Critics have also charged sociobiology with producing “just-so stories”: plausible narratives about how a trait might have evolved, dressed up as proof that it actually did. The charge lands hardest on human behavior, where the ancestral environment cannot be directly observed.

It lands far less on the animal studies above. Each of those made a specific prediction that could have failed and did not.

Contemporary Research

Curry, Mullins, and Whitehouse (2019) asked a sharp question: is cooperation itself judged morally good across cultures? Evolutionary theory predicts yes, if moral judgment tracks real solutions to cooperation problems.

A second study asked a sharper version of Wilson’s original, most contentious claim. Do genes predict social class?

Together, the two studies update the debate rather than settle it. Neither extreme survives intact. The genetic correlate is real, but it works through people’s own choices and migration, not direct genetic determination.

References

Alcock, J. (2001). The triumph of sociobiology. Oxford University Press.

Alexander, R. D. (1979). Darwinism and human affairs. University of Washington Press.

Cronin, H. (1993). The ant and the peacock: Altruism and sexual selection from Darwin to today. Cambridge University Press.

Daly, M. (2015). Sociobiology: Overview. In J. D. Wright (Ed.), International encyclopedia of the social & behavioral sciences (2nd ed., Vol. 22, pp. 908–911). Elsevier.

Daly, M., & Wilson, M. (1988). Evolutionary social psychology and family homicide. Science, 242(4878), 519-524.

Darwin, C. (1859). On the origin of species.

Faragalla, K. M., Chernyshova, A. M., Gallo, A. J., & Thompson, G. J. (2018). From gene list to gene network: Recognizing functional connections that regulate behavioral traits. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 330(6-7), 317-329.

Frank, R. (1988). Passions within reason: The strategic role of the emotions. New York, NY: Norton

Gardner, A., West, S.A., Wild, G. (2011). The genetical theory of kin selection. Journal of Evolutionary Biology 24, 1020–1043.

Griffin, A. S., & West, S. A. (2003). Kin discrimination and the benefit of helping in cooperatively breeding vertebrates. Science, 302(5645), 634-636.

Griffiths, P. E., & Gray, R. D. (2001). Darwinism and developmental systems. Cycles of contingency: Developmental systems and evolution, 195-218.

Haig, D. (2002). Genomic imprinting and kinship. Rutgers University Press.

Hamilton, W.D. (1964). The genetical evolution of social behavior, I and II. Journal of Theoretical Biology 7, 1–16, 17–52.

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Krupp, D.B., DeBruine, L.M., Jones, B.C. (2011). Cooperation and conflict in the light of kin recognition systems. In: Salmon, C.A., Shackleford, T.K. (Eds.), The Oxford

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James D. Wright (2015), International Encyclopedia of the Social & Behavioral Sciences (Second Edition). Elsevier.

Lumsden, C. J. (2011). Signs of the times: Mind, evolution, and the twilight of postmodernity.

Queller, D.C. (2011). Expanded social fitness and Hamilton’s rule for kin, kith, and kind. Proceedings of the National Academy of Sciences USA 108, 10792–10799.

Scott, J. P. (1950). The social behavior of dogs and wolves: an illustration of sociobiological systematics. Annals of the New York Academy of Sciences, 51(6), 1009-1021.

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Trivers, R. L. (1971). The evolution of reciprocal altruism. Quarterly Review of Biology, 46(1), 35-57.

Trivers, R.L. (1972). Parental investment and sexual selection. In: Campbell, B. (Ed.), Sexual Selection and the Descent of Man 1871–1971. Aldine, Chicago, pp.
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Weinrich, J. D. (1980). Toward a sociobiological theory of the emotions. In Theories of Emotion (pp. 113-138). Academic Press.

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Wilson, E. O. (1975). Sociobiology: The new synthesis. Harvard University Press.

Further Information

• Sociobiology MIT Lecture Notes
• Sociobiology Book