Our results tentatively suggest that SOB has a different, but related, psychological impact than dopamine D2/D4 receptor genetic polymorphisms on several behavioral phenotypes. This study replicates the past findings that winter-borns are more sensation seeking, but differs in that the association was only evident in males. SOB was unrelated to several behavioral/psychological phenotypes that were associated with DRD2 and DRD4 genetic polymorphisms. But, including SOB in factorial models revealed a previously unobserved association and evidence of moderation of DRD4 expression by SOB. These results must be viewed with caution as the number of phenotypic dependent variables analyzed here may have increased the risk of type I errors. An adaptive basis for the associations found here and in other studies of SOB is not clear. The behavioral implications of SOB remain ambiguous and its interactions with genotype effects are tentative. To further dissect the association of season of birth with later behaviors, more comprehensive analysis including experimental variations of photoperiod in lab animals in utero and early in life, and analysis of light exposure of pregnant women and later their young
