Behavioral genetics and evolutionary psychology: Unified perspective on personality research

Human Biology, Apr 1998 by Segal, Nancy L, MacDonald, Kevin B

Adoption Design. Adoption studies include unrelated individuals raised together or biological relatives living apart. Behavioral resemblance between unrelated individuals living together is associated with common environmental factors. Similarity between biological relatives raised apart is associated with their common genes, given an absence of correlated trait-relevant rearing environments. Problems associated with adoption designs, such as selective placement (i.e., congruence between features of the biological and nonbiological families), are described by Plomin et al. (1997) and Turkheimer (1991).

Heritability. Heritability refers to the proportion of trait variation associated with genetic differences among people. Broad heritability includes additive and nonadditive components. Additive components result from summing effects across many different genes, whereas nonadditive components result from interactions among many different genes. It is the additive component on which selection operates and which is responsible for parent-child resemblance; this is termed narrow heritability. Heritability estimates are not fixed values, nor do they imply fixity of the trait. When members of a population experience similar environments, heritability increases; when interindividual environments are less similar, heritability decreases.

Gene-Environment Interaction. Gene-environment interaction refers to differential behavioral or physical outcomes produced by particular combinations of genes and environments. Not all genotypes show similar expression in a given environment; for example, one individual may thrive in a stimulating setting, while another may do poorly.

Gene-Environment Correlation. Gene-environment correlation refers to associations between genotypes and environments. Passive gene-environment correlation describes transmission of correlated genes and environments from parents to children. Active gene-environment correlation refers to individuals seeking out people, places, and experiences compatible with their genetically based tendencies. Reactive gene-environment correlation describes elicitation of responses from others based on individuals' own genetically based characteristics.

Behavioral Genetics and Evolutionary Theory. Several investigators have applied twin and adoption methods to specifically assess evolutionarybased hypotheses. Evolutionary theory offers behavioral genetics (and virtually all subdisciplines within the psychological field) a new theoretical framework for formulating hypotheses, designing experiments, and interpreting findings (Wilson et al. 1996; Segal 1997b). This section provides a sampling of available studies and suggestions for future analyses.

Studies Based on Inclusive Fitness Theory. An important link between behavioral genetics and evolutionary theory is inclusive fitness theory (Hamilton 1964). Hamilton reasoned that natural selection favors alleles predisposing individuals to behave in ways that favor preservation of those alleles in future generations. Behaviors that enhance the reproductive fitness of close relatives, even at cost to the benefactor, facilitate representation of shared genes, a concept called inclusive fitness. Behaviors that reduce the reproductive fitness of individuals may thus be selected if those behaviors increase the fitness of relatives. This theory and the body of work that flows from it have yielded novel perspectives on play (Fagen 1987), psychiatric disorder (McGuire et al. 1994), suicide (de Catanzaro 1995), sociopathy (Mealey 1995), maternal investment (Mann 1992), resource utilization (Charlesworth 1996), and other behaviors.