levels of ACTH 10. We examined behavioral dimensions during infancy and found that carriers of the -2232 G allele were more “Exploratory/bold,” exhibiting relatively high levels of environmental exploration and aggression. We also employed a challenge that has been developed to test behavioral responses to social intrusion in adolescent or adult primates. This test is not only an excellent tool for looking at coping responses during exposures to social stress, but is especially useful for assessment of individual differences in behavioral inhibition, as approaching an unfamiliar animal is considered to be a risky and impulsive behavior 35. Consistent with the fact that G allele carriers rated higher on the exploratory/bold dimension during infancy, we found that male G allele carriers exhibited a more bold and active response to an unfamiliar intruder. An individual that readily approaches novel objects or conspecifics may do well in certain social situations, but may face higher risk of predation or attack than a more cautious, harm-avoidant individual. Such behaviors might, therefore, be predicted to confer selective advantage at particular developmental or life history stages and in certain environmental contexts.
