@Mephi Wikipedia: Prenatal hormones and sexual orientation#Male homosexuality as hypermasculineHomosexuelle haben höhere Testosteronwerte und auch größere Penisse als Heterosexuelle.
The levels of plasma testosterone of 19 young male homosexuals (Kinsey group VI) were found to be significantly higher (p < .01 ) than those of 20 strictly heterosexual men matched for average age.
http://ajp.psychiatryonline.org/article.aspx?volume=131&page=82It has been suggested that the greater the number of older male siblings the higher the level of androgen fetuses are exposed to.
Das würde auch deiner Aussage mit dem Östrogen, welches Männer homosexuell werden lasse, widersprechen.
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Das mit den älteren Brüdern stimmt tatsächlich, aber nur wenn man Rechtshänder ist. Man nennt es den "Fraternal Birth Order Effect".
Specifically, older brothers increased the odds of homosexuality in right-handers only; in non-righthanders, older brothers did not affect the odds of homosexuality.
http://www.ncbi.nlm.nih.gov/pubmed/17907817Allerdings gibt es auch zu dieser Theorie Widerspruch.
For men, I find that having one older brother does not raise the likelihood of homosexuality.
Although having multiple older brothers has a positive coefficient, it is not significant.
http://www.ncbi.nlm.nih.gov/pubmed/18937128