[ExI] sex - was Re: The smart-stupid dimension

SR Ballard sen.otaku at gmail.com
Sun May 21 09:08:17 UTC 2017


Male Homosexuality

http://www.pnas.org/content/103/28/10771

"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."

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https://www.cambridge.org/core/journals/journal-of-biosocial-science/article/relation-of-birth-order-to-sexual-orientation-in-men-and-women/31B99DDC5BE81454D318706DAC3C0728

"Homosexual men have a higher mean birth order than do heterosexual
men, primarily because they have a greater number of older brothers.
The purpose of this study was to determine whether the same difference
occurs in homosexual vs heterosexual women."

(short answer, no, it doesn't)

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http://www.sciencedirect.com/science/article/pii/S0191886900000519

"Several studies have shown that older brothers increase the
probability of homosexuality in later-born males. The maternal immune
hypothesis proposes that this phenomenon reflects the progressive
immunization of some mothers to Y-linked minor histocompatibility
antigens (H–Y antigens) by each succeeding male fetus"

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http://www.sciencedirect.com/science/article/pii/S0018506X05002138

"The present study investigated evidence for an interaction between
two of the best established etiologic factors, or markers of etiologic
factors, in the literature on male homosexuality: fraternal birth
order and hand preference."

This one is pretty interesting.

-

So it may be that we evolved this way because the mother already had
enough male offspring, and continuing to have heterosexual male
offspring may have introduced too much competition. Or as was said,
because males without offspring can attend to other social duties and
needs, and so they increase the passage of the genes of their
relatives.




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