Blackwell Reference Online

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People differ on a variety of dimensions: Some are aggressive, others meek; some are liberal, others conservative; some are smart, others dull. How are we to understand these differences? The science of behavioral genetics approaches the problem by assuming that there are two sources of influence for all dimensions of variability among people: Each individual has an inherited or biologically transmitted genetic endowment and each individual develops in a set of environmental circumstances. Thus, observed differences between people, i.e., differences in phenotype, are due to differences in their genetic makeup, i.e., differences in genotype, or differences in their environment, or both. Psychological entitites such as personality and attitudes are subject to this same analysis. The most common index of the importance of genetic influence is known as heritability. It is defined as the proportion of variance in phenotype that is due to variance in genotype in a particular population. Heritability has no absolute biological meaning and fluctuates with the population sampled. If both genetic and environmental influences are important then populations with restricted environments will produce greater heritability estimates than populations with large environmental differences; heritability estimates will be lower in genetically homogeneous populations then in genetically diverse populations. ... log in or subscribe to read full text