Behavior genetic differences within and between defined human populations.

The small populations of the Caucasus offer a unique opportunity to consider concepts, such as heritability, which are often considered properties of a trait but which are really properties of a population. A comprehensive strategy is outlined for studying intra- and interpopulation genetic structure across a wide range of traits and environments. A three-way association is demonstrated between 12 of 16 psychophysiological traits, attitude, and the t allele for PTC sensitivity. Differences between populations and traits are evaluated in theoretical terms for morphological, physiological, and psychological measures. While decreases in performance with inbreeding are often predicted, in these small, isolated populations the effects are minimal.