Sensation seeking in females from opposite- versus same-sex twin pairs: hormone transfer or sibling imitation?

The aims of this study were to replicate the results of a previous study (Resnick et al. 1993) and to extend them by examining the evidence for prenatal exposure to androgens versus sibling imitation as a potential cause of group differences in levels of sensation seeking. Participants were members of the Australian Twin Registry who had participated in a structured interview study and completed the Zuckerman Sensation-Seeking Scale. Three sets of group comparisons were conducted: (1) the sensation seeking scores of females from same-sex twin pairs (n = 1,947) were compared to females from opposite-sex twin pairs (n = 564), (2) females from same-sex twin pairs without a brother (n = 580) were compared to same-sex females with a close-in-age older brother (n = 300), and (3) same-sex females who had a close-in-age older brother (n = 300) were compared to females from opposite-sex twin pairs (n = 564). Females from opposite-sex twin pairs obtained significantly higher scores than females from same-sex twin pairs on the experience-seeking (d = 0.12) and thrill and adventure seeking (d = 0.10) subscales, but not the boredom susceptibility (d = -0.01) or disinhibition (d < 0.01) subscales of the Sensation-Seeking Scale. The modest effects obtained could not be explained by the psychosocial effect of having a close-in-age brother. Considering these effects alongside the overall sex differences in the Sensation-Seeking Scales of experience-seeking (d = 0.12 vs. d = 0.18) and thrill and adventure-seeking (d = 0.10 vs. d = 0.83) suggests that prenatal androgens may actually play a large role in the sex difference in the personality trait of experience seeking, and a smaller role in thrill and adventure-seeking; there was no evidence from this study that prenatal androgens are important for explaining sex differences in the traits of boredom susceptibility or disinhibition.