Behavior Genetics

Behavior Genetics is a theory and a method that focuses on the genetic and environmental factors that contribute to individual differences in the population. Many aspects of intellectual functioning, personality, health, and well-being across the lifespan show at least some genetic influence. Beyond just assessing the role of heredity, these methodologies are some of the most powerful tools for understanding environmental influences on behavioral development. This entry illustrates the kinds of questions that can and cannot be addressed with these methodologies, describes the types of research designs used, explains the link with molecular genetics, highlights controversies with the lifespan development perspective, and discusses the ways in which developmental scientists and behavioral geneticists can unite to advance both fields.

There are two ways to think about development across the lifespan. The first focus is on normative development, which incorporates (a) the general laws of development—that is, why humans use language; (b) the description of the typical developmental trajectory—for example, what verbal abilities children should have at a certain age; (c) the identification of group differences—such as why, on average, girls develop verbal abilities sooner than boys.

The second approach to understanding development (including the behavioral genetic perspective) centers on the individual, to explore the etiology (i.e., the underlying cause or reason for something) of individual differences from both the average course of development and from other individuals in the population, addressing questions such as these: Why do individuals differ on tests of verbal ability? Why are some people better at learning multiple languages? In the case of the behavioral genetic approach, that variability is then attributed to nature (role of heredity) or nurture (influence of the environment).

This distinction is important to understand, because the etiology of normative development or group differences may be very different from the etiology of individual differences; that is, normative behavior may be due to genetic factors, whereas individual differences may be due to the influence of the environment. Of additional importance to a developmental perspective, genes turn on and off across development, so the genes that are central to development at one point in the lifespan may be different from those that are prominent later.

It is also important to underscore what it means to say that there are genetic influences on attributes of interest, such as memory, shyness, or feelings of depression. Although there are many single-gene disorders, there is no example of a behavioral phenotype governed by a single gene. A phenotype is the term used to represent the organism’s observable characteristic or trait; from a behavioral perspective, examples include attributes such as conscientiousness, math aptitude, or anxiety. Hence, it is no surprise that multiple genes influence such complex behaviors as well as by the environment.

Furthermore, genes are blueprints that are translated into the assembly and regulation of proteins; these proteins then interact with other physiological intermediaries—such as other proteins, hormones, or neurotransmitters—and with environmental factors. So we should think of genetic influences as propensities that may nudge development in one direction rather than another and not in a deterministic way. Consider alcoholism as an example; we know that alcoholism runs in families and it is possible to breed mice to be extremely sensitive to ethanol, which supports the notion that alcoholism is hereditary.

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