Behavior geneticist Eric Turkheimer set out three laws of behavior genetics, Charles Murray reminds us (in Human Diversity: The Biology of Gender, Race, and Class):

First law : All human behavioral traits are heritable. Second law : The effect of being raised in the same family is smaller than the effect of genes. Third law : A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families.

Murray adds some related findings:

Whether the topic was a Big Five characteristic such as extraversion or neuroticism or more specific characteristics such as tolerance, sense of well-being, or alienation, twin studies of heritability kept coming up with correlations for MZ twins that were more than twice the correlations for DZ twins, leaving no role for the shared environment.

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The literature on shared environment, nonshared environment, and heritability tells us that a family’s SES (income, parental education and occupation) is unimportant in explaining the cognitive abilities and personality traits that parents try hardest to promote.

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The bulk of the variance in success in life is unexplained by either nature or nurture. Researchers are lucky if they explain half of the variance in educational attainment with measures of abilities and socioeconomic background. They’re lucky if they can explain even a quarter of the variance in earned income with such measures. The takeaway for thinking about our futures as individuals is that we do not live in a deterministic world ruled by either genes or social background, let alone by race or gender.