Molecular investigations into complex behavior: lessons from sexual orientation studies.

A review of recent molecular genetic investigations into sexual orientation is presented and used as a model to identify unique challenges encountered in research on complex behavior. Five main themes are presented that are generally applicable to most behavioral genetics investigations: (1) A precise definition of the phenotype that, as much as possible, unambiguously differentiates the study group from the control group must be achieved; (2) environmental and social contributions to a trait may exhibit significant sex differences; (3) subsets within the study sample may reveal important information about genetic and environmental contributions to the trait that otherwise would be missed; (4) the high degree of specificity required to define a study sample severely restricts the application of results to general populations; and (5) studies attempting to replicate data must strictly parallel the original methodology if valid comparisons are to be made.