Behaviors distinguish human beings from other creatures and from each other. Genetic perspectives could help account for both the universals of human behavior (those shared by all) and the particulars (the individual differences). Behaviors are among the most complex attributes to study, but developments in behavioral genetics and the human genome project are producing new insights in this important area of study.
Behavioral genetics is a field that uses genetic methods to answer three questions about the nature and origin of individual differences in behavior: Is there good evidence for genetic influence on behavioral differences? How strong is this effect? Through what mediating steps do the genes influence the behavior? The manner in which such issues are addressed may have significant implications for one's conceptions of human nature, ethical responsibility, and freedom.
To answer these questions, behavioral geneticists use a variety of methods to study cognitive abilities, personality traits, psychiatric disorders, and other conditions. For example, results from family, twin, and adoption studies are carefully compared in order to analyze the differential effects of genetic background and rearing circumstances on the risk of specific behaviors in the offspring. Since the mid-1990s, the insights and methods developed in the human genome project have begun to shed light on the molecular pathways involved in brain development and function. This knowledge in turn may lead to better methods of intervention or treatment that are adapted to an individual's genetic makeup.
Such a strategy differs from that used in two other approaches. Behaviorism arose as a protest against introspective psychology and emphasized observable behavior in response to environmental stimuli, thus implying that behavior is shaped entirely by environmental forces. Sociobiology, on the other hand, emphasizes the role of an evolved, species-typical, nature for the behavior of a given organism.
Behavioral geneticists accept the view that behavior is influenced by both nature and nurture, but recent studies have shown that these components are not as independent as they were once thought to be. Some genes influence the way individuals select and shape experiences, while other genes can affect an individual's susceptibility to these experiences. Careful research designs are needed to sort out such gene/environment interactions and correlations.
Contrary to reports of a "novelty-seeking gene" or a "schizophrenia gene," researchers do not expect to find a single gene that explains a specific behavior (except in rare cases). Instead, multiple genes are associated with aspects of brain functioning that mediate one's preferences and capacities; these in turn influence one's likelihood of showing that behavior. In such situations any specific gene is likely have only a small effect.
Genetic research methodology may be inherently reductionistic, but this need not lead to explanatory reductionism. Genes never act in isolation, and their effects must always be interpreted in context. Individual genes can be turned on or off in response to signals from their environment, with the result that gene expression can even be modified indirectly by social interaction.
Clearly any evidence that DNA defines human beings and shapes their decision-making would appear to be incompatible with traditional understandings of human freedom and moral responsibility. The findings from behavioral genetics, however, indicate that genetic influences should be understood more as predispositions or limiting factors. An individual's genome may set boundaries on various traits and potential, but it does not determine how one will organize his or her life within those parameters.
In summary, genes are necessary for human existence and give people the ability to express those qualities that are distinctively human. Genes are not sufficient to account for all differences in behavior, however, since interactions with environment and individual experience are involved throughout life. An adequate view of human nature should be informed by an understanding of the effects of genes at many levels. Future research is likely to provide further evidence of the contributions of genes to psychological, social, moral, and religious behaviors.
See also Behaviorism; Sociobiology
anderson, v. elving. "a genetic view of human nature." in whatever happened to the soul? scientific and theological portraits of human nature, warren s. brown, nancey murphy, and h. newton malony, eds. minneapolis, minn.: fortress press, 1998.
chapman, audrey r. unprecedented choices: religious ethics at the frontiers of genetic science. minneapolis, minn.: fortress press, 1999.
cole-turner, ronald. the new genesis: theology and the genetic revolution. louisville, ky.: westminster and john knox press, 1993.
peters, ted, ed. genetics: issues of social justice. cleveland, ohio: pilgrim press, 1998.
plomin, robert; defries, john c.; mcclearn, gerald e.; and mcguffin, p., eds. behavioral genetics, 4th edition. new york: w. h. freeman, 2000.
v. elving anderson
audrey r. chapman