Sex Ratio of Older Siblings in Heterosexual and Homosexual, Right-Handed and Non-Right-Handed Men
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This study investigated why older brothers, which increase the odds of homosexuality in later-born males who are right-handed, have no effect or the opposite effect on later-born males who are non-right-handed. The specific question was whether the different results for the non-right-handed men have to do with the heterosexual non-right-handers or the homosexual non-right-handers. The human sex ratio at birth (106 males per 100 females) was used as a gold standard for determining which groups differ from the general population and in which direction. All usable data from previous studies were combined to obtain the largest possible sample (N = 8,201). The observed ratio of older brothers to older sisters was 105 for the heterosexual right-handers, 128 for the homosexual right-handers, 127 for the heterosexual non-right-handers, and 96 for the homosexual non-right-handers. The ratios for the homosexual right-handers and the heterosexual non-right-handers differed significantly from the expected value. These results suggest that both heterosexual and homosexual non-right-handers contribute to the older brothers × handedness × sexual orientation interaction.
KeywordsAdaptation Birth order Evolution Handedness Homosexuality Older brothers Reproductive fitness Sexual orientation Sinistrality
- Blanchard, R., & Lippa, R. A. (in press-a). The sex ratio of older siblings in non-right-handed homosexual men. Archives of Sexual Behavior. DOI: 10.1007/s10508-006-9107-6.Google Scholar
- Blanchard, R., & Lippa, R. A. (in press-b). Birth order, sibling sex ratio, handedness, and sexual orientation of male and female participants in a BBC Internet research project. Archives of Sexual Behavior.Google Scholar
- Bogaert, A. F., Blanchard, R., & Crosthwait, L. E. (2006). Interaction of birth order, handedness, and sexual orientation in the Kinsey interview data. Manuscript in preparation.Google Scholar
- James, W. H. (1987). The human sex ratio: Part 1. A review of the literature. Human Biology, 59, 721–752.Google Scholar