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Older brothers increase chance of a man being gay September 7, 2009

Posted by Geekgirl in Developmental, genetics, in the womb, sexual orientation.
Tags: , , ,

Many studies have been done on gay men and older brothers. The more older brothers that a man has, the more likely it is that he will be gay. These researchers looked at whether the effect is due to biological brothers only or all brothers, including nonbiological brothers (as in mixed families). The abstract is quite short but gets right to the point. The entire paper can be found online at the Proceedings of the National Academy of Sciences.

Care to guess the answer?


Biological versus nonbiological older brothers and men’s sexual orientation

  1. Anthony F. Bogaert*

+Author Affiliations

  1. Departments of Community Health Sciences and Psychology, Brock University, St. Catharines, ON, Canada L2S 3A1
  1. Edited by Dale Purves, Duke University Medical Center, Durham, NC, and approved May 17, 2006 (received for review December 29, 2005)


The most consistent biodemographic correlate of sexual orientation in men is the number of older brothers (fraternal birth order). The mechanism underlying this effect remains unknown. In this article, I provide a direct test pitting prenatal against postnatal (e.g., social/rearing) mechanisms. Four samples of homosexual and heterosexual men (total n = 944), including one sample of men raised in nonbiological and blended families (e.g., raised with half- or step-siblings or as adoptees) were studied. Only biological older brothers, and not any other sibling characteristic, including nonbiological older brothers, predicted men’s sexual orientation, regardless of the amount of time reared with these siblings. These results strongly suggest a prenatal origin to the fraternal birth-order effect.



1. Babys Postnatal Care and advice - September 17, 2009

[…] Older brothers increase chance of a man being gay […]

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