Graduation Year


Document Type




Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department


Major Professor

Marina A. Bornovalova, Ph.D.

Committee Member

Mark Goldman, Ph.D.

Committee Member

Jack Darkes, Ph.D.

Committee Member

Stephen Stark, Ph.D.

Committee Member

Brent Small, Ph.D.


externalizing, fetal, prenatal, testosterone, twin


Fetal testosterone (FT) exposure influences sexual differentiation and may promote well-established sex differences in externalizing (EXT) behavior. Although puberty may be a critical period for these effects, it is unknown how FT exposure influences EXT as a function of pubertal development. We used a longitudinal, multi-sample design to test the relationships between two proxy indices of FT exposure and EXT as a function of age and pubertal development (approximately ages 6, 9, 11, 14, and 16). Twin data were used to approximate FT exposure (TT-FT) because testosterone is thought to cross the intrauterine membrane and cause variability in co-twin gonadal hormone exposure, with increasing exposure for males and participants with male co-twins. Increasing number of older siblings may also approximate increasing FT exposure (SI-FT), although existing research has yet to disentangle possible postnatal socialization effects from potential FT exposure using this variable. Given that biologically related siblings share a fetal and social environment while non-biologically related siblings simply share a social environment, we tested the independent effect of SI-FT on EXT using a sibling adoption design. Across four independent samples, SI-FT and TT-FT predicted externalizing for males alone. SI-FT predicted EXT over-and-above socialization influences and interacted with pubertal development in two independent samples, with elevated EXT for those in mid-late puberty that were exposed to increased FT. TT-FT predicted EXT differentially as a function of developmental period. Our data are consistent with the notion that exposure to FT promotes sexually differentiated, sexually selected behavior during reproductively relevant periods.