Chapter Review

Behavioral genetics concerns the degree to which personality is inherited from parents and shared among genetic relatives.

Evolutionary psychology concerns the ways in which human personality (and other behavioral propensities) may have been inherited from our distant ancestors, and how these propensities have been shaped over the generations by their consequences for survival and reproduction.

Behavioral Genetics

Behavioral genetics has always been controversial because of its historical association with eugenics (selective breeding), the concept of cloning, and the belief that it implies people’s fate is set at birth, but none of these ideas is part of modern thinking on this topic.

The most commonly used heritability coefficient is calculated as the correlation across pairs of monozygotic twins for that trait, minus the correlation across dizygotic twins, times two: heritability quotient = (rMZrDZ) × 2.

Heritability statistics computed from the study of monozygotic and dizygotic twins estimate that about 40 percent of the phenotypic variance in many personality traits can be accounted for by genotypic variance.

Genes interact rather than simply expressing the sum total of their effects.

Heritability studies confirm that genes are important for personality, can be informative about whether psychological disorders are distinct pathologies or extremes on the normal range of variation, and, perhaps most importantly, can provide insights into the effects of the environment on behavior and personality.

Findings that unrelated adopted children who grow up together do not develop similar personalities led to questioning whether the family environment affects development. More thorough analyses and new data, however, suggest that the shared family environment affects many important traits, especially when they are measured via behavioral observation rather than self-report.

While studies of heritability are informative, the heritability statistic is not the "nature-nurture ratio" because traits completely under genetic control often have low or zero heritabilities.

Recent research is beginning to map out the complex route by which genes determine biological structures that can affect personality. For example, the DRD4 gene is associated with dopaminergic systems that play a role in the trait of extraversion, and the 5-HTT gene is associated with the neurotransmitter serotonin, and with the trait of impulsivity and related patterns of behavior. The amygdala in people with the short-form allele of this gene responds more strongly to unpleasant stimuli; these people are at risk for anxiety disorders.

While research has begun to document the relationships among genes, brain function, and personality, the situation is even more complex than these relationships: Not only do genes interact with each other, but their effects on development are also critically influenced by the environment. For example, people with the short allele for the 5-HTT gene (which affects serotonin) appear to be at risk for depression and antisocial behavior, but only if they experience severe stress or maltreatment in childhood.

Now that it is established that genes matter for personality and life outcomes, and that almost "everything is heritable," the future of behavioral genetics research lies not in calculating heritabilities, but in understanding the interactions among genes and between genes and the environment that affect personality traits and life outcomes.

Not all findings concerning gene-personality correlations or gene-environment interactions are consistently replicated, leading some critics to portray the entire enterprise as misguided. But such a conclusion is surely premature; the field of molecular behavioral genetics is still in its very early stages and much remains to be learned.

Evolutionary Personality Psychology

Evolutionary psychology attempts to explain behavioral patterns by analyzing how they may have promoted survival and reproduction in past generations.

Evolutionary psychology has considered aggression and altruism in terms of their necessary role for survival and also the potential disadvantages of these behaviors.

Self esteem may be a "sociometer," according to Mark Leary’s theory, that assesses the degree to which one is accepted by the group. A decline in self-esteem might be an evolved danger signal that one may be shunned.

Depression may have evolved as a way to prevent wasting energy on fruitless endeavors and as a means of seeking social support.

Evolutionary psychology has paid special attention to sex differences in mating behaviors, including differences in what men and women find most attractive in each other and the strategies they use to seek and keep mates. For example: Men high in "sociosexuality"—the willingness to engage in sexual relations in the absence of a meaningful relationship—are more accurate in assessing their own "mate value" than men low in this trait, and are more likely to use symbols of "conspicuous consumption" to attract women. Women appear to understand this tactic, however. Additionally, men seem to be more jealous about sexual than emotional infidelity compared to women, and women show the reverse pattern. However, this is a relative difference: Both kinds of infidelity are unpopular with both sexes.

Individual differences are important in evolutionary psychology because: For a species to remain viable, it must include diversity. A trait that is adaptive in one situation may be fatal in another; behavioral patterns have evolved to emerge as a function of environmental experience; evolution may have provided people with several possible strategies, and they use the one that makes the most sense given their circumstances; and some biologically influenced behaviors may be "frequency dependent," meaning that they adjust according to how common they are in the population at large.

Controversies over evolutionary psychology provide five "stress tests" for the theory. The key issues are: the methodology of evolutionary theorizing; the degree to which people are consciously aware of following evolutionary strategies to promote survival and reproduction; the belief by some that evolutionary explanations imply social change is impossible or must be slow; the question of whether people have evolved specific behavioral "modules" or a broader capacity to respond flexibly to environmental demands; and the question of whether behavioral patterns attributed to evolutionary biology might be better explained by social structure.

One of the most important contributions of evolutionary theory may be that psychologists are now obligated to consider how the behavioral patterns they uncover may have been adaptive to the species over evolutionary history.

Inheritance Is the Beginning, Not the End

The biological aspects of personality that you inherited from your parents may determine your psychological starting point, but not your life outcomes.

Will Biology Replace Psychology?

Some observers speculate that increases in knowledge will someday allow all psychological processes to be explained in terms of biology, a position called biological reductionism.

However, biology will never replace psychology because biology does not and cannot, by itself, address many core psychological issues. These issues include the ways people act in their daily social environments, the basis of behavioral consistency, the experience of psychological conflict, the ways people interpret their environments and plan strategies for success, and many others.