A test of the maternal stress hypothesis for human male homosexuality
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Recent evidence implicates a biological, and particularly, a neurohormonal role for the etiology of human male homosexuality. In contrast to most other traits, however, there is a priori reason to doubt high heritability of differences in sexual orientation, due to the presumed selective disadvantage of homosexuality. The discovery that prenatal stress behaviorally feminizes male offspring in rats has been of great interest as a plausible environmental model which could account for the neural feminization required by the neurohormonal theory of male homosexuality. Dorner has presented evidence suggesting a strong maternal stress effect for human male homosexuality; however, his methodology was grievously flawed. The maternal stress hypothesis was tested using mothers' retrospective reports of events during pregnancy. Such reports were obtained from 83 mothers of nonheterosexual males (Kinsey Fantasy Scores [greater than or equal to] 3; 72 of these subjects were Kinsey 5s or 6s.), 60 mothers of heterosexual males (Kinsey Fantasy scores < 3), 53 mothers of heterosexual females, and 19 mothers of female nonheterosexuals. A within-family analysis was also done, as mothers also rated stress for their pregnancies with heterosexual siblings of subjects. Results of both between-family and within-family analyses were strikingly negative for males. Unexpectedly, however, there was a significant correlation between sexual orientation and prenatal stress for females, with mothers of nonheterosexual females reporting greater stress. An additional analysis of maternal stress-proneness provided some support for a modified maternal stress hypothesis: Stress-proneness in mothers (measured by personality scales) correlated positively and significantly with childhood effeminacy of male offspring. This correlation was negligible for females. While not disproving the maternal stress hypothesis, results of this study are not consistent with a strong effect of maternal stress on male sexual orientation. Because male homosexuality is strongly familial (confirmed in the present study), it is recommended that genetic explanations should be pursued more vigorously.