W. W. Norton & Company | The Personality Puzzle, 4th ed.

CHOOSE A CHAPTER

Chapter 9: The Inheritance of Personality: Behavioral Genetics and Evolutionary Theory

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 were shaped over the generations by their consequences for survival and reproduction.

Behavioral genetics has always been controversial because of its historical association with eugenics (selective breeding) and the concept of cloning, but modern behavioral geneticists (mostly) disavow any interest in these goals.

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 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. Other studies suggest the real figure may be lower because 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 distinctive 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, but recent analyses and new data suggest that the shared family environment affects many important traits, especially when they are measured via behavioral observation rather than self-report.

Recent research is beginning to map out the complex route by which genes determine biological structures that can affect personality; for example, the D4DR gene is associated with dopaminergic systems that play a role in the trait of extraversion. Another example is research showing that people with the short-form allele of a gene affecting serotonin function have stronger responses in their amygdalas to unpleasant stimuli, and are at risk for anxiety disorders.

While research has begun to document relations between genes, brain function, and personality, the situation is actually even more complex. Not only do genes also interact with each other, but their effects on development are also critically influenced by the environment. For example, people with the short-form gene that affects serotonin function appear to be at risk of depression and anti-social behavior, but only if they experience severe stress or maltreatment in childhood.

Evolutionary psychology attempts to explain behavioral patterns—such as aggression, altruism, depression, mating choices, and sex differences—by analyzing how they may have promoted survival and reproduction in past generations.

Some of these explanations are controversial, and a key issue concerns the degree to which evolutionary processes have produced specific modular patterns of human behavior, as opposed to general abilities to understand and flexibly respond to changing environmental factors, including culture. Either way, research on evolutionary biology and behavioral genetics implies that biology and genetic inheritance are involved in determining personality.

Evolutionary psychology explains individual differences as the results of interactions with the environment. In that sense, human nature may have evolved to be flexibly adaptive to specific circumstances.

As exemplified by Bem's theory of the development of sexual orientation, the promise of biological approaches to personality study comes from their potential to illuminate the interactions between biological, psychological, social, and sociological influences on behavior.

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