Höhere Fruchtbarkeit der weiblichen Verwandten als Vorteil der Homosexualität und der Bisexualität?

Ein eigener Artikel über Homosexualität lässt leider noch etwas auf sich warten, aber ich bin gerade über diese Studien gestolpert, die ich recht interessant finde. Es geht darum, inwieweit die weiblichen Verwandten von Homosexuellen und Bisexuellen fruchtbarer sind, was ein Vorteil wäre, der zur Vererbung entsprechender Gene führen könnte, insbesondere wenn es solche sind, die in Frauen wirksam werden:

Studie 1:


Recent studies on male homosexuals showed increased fecundity of maternal female relatives of homosexual probands, compared to those of heterosexual controls. We have suggested that these data could be explained by the transmission, in the maternal line, of an X-linked genetic factor that promotes androphilic behavior in females and homosexuality in males.


Our original studies were on relatives of male subjects who declared themselves to be exclusively homosexual. However, the relationship between homosexuality and bisexuality, including the possibility of shared genetic factors, is complex and largely unexplored. To cast light on this issue, in the present study we examined whether relatives of bisexuals show the same indirect fitness advantage as previously demonstrated for homosexuals.


Subjects completed a questionnaire on their sexual orientation, sexual behavior, and their own and their relatives‘ fecundity.


We studied 239 male subjects, comprising 88 who were exclusively or almost exclusively heterosexual (pooled to comprise our „heterosexual“ group), 86 who were bisexual, and 65 exclusively or almost exclusively homosexual individuals (pooled in our „homosexual“ group). Bisexuals were here defined on the basis of self-identification, lifetime sexual behavior, marital status, and fecundity.


We show that fecundity of female relatives of the maternal line does not differ between bisexuals and homosexuals. As in the previous study on homosexuals, mothers of bisexuals show significantly higher fecundity, as do females in the maternal line (cumulated fecundity of mothers, maternal grandparents, and maternal aunts), compared to the corresponding relatives of heterosexual controls.This study also shows that both bisexuals and homosexuals were more frequently second and third born. However, only homosexuals had an excess of older male siblings, compared to heterosexuals.


We present evidence of an X-chromosomal genetic factor that is associated with bisexuality in men and promotes fecundity in female carriers.

Quelle: Genetic factors increase fecundity in female maternal relatives of bisexual men as in homosexuals

Die zweite Studie ist teilweise von den gleichen Forschern, sie hat Familiengeschichten aufgeschlüsselt:

here is a long-standing debate on the role of genetic factors influencing homosexuality because the presence of these factors contradicts the Darwinian prediction according to which natural selection should progressively eliminate the factors that reduce individual fecundity and fitness. Recently, however, Camperio Ciani, Corna, and Capiluppi (Proceedings of the Royal Society of London, Series B: Biological Sciences, 271, 2217-2221, 2004), comparing the family trees of homosexuals with heterosexuals, reported a significant increase in fecundity in the females related to the homosexual probands from the maternal line but not in those related from the paternal one. This suggested that genetic factors that are partly linked to the X-chromosome and that influence homosexual orientation in males are not selected against because they increase fecundity in female carriers, thus offering a solution to the Darwinian paradox and an explanation of why natural selection does not progressively eliminate homosexuals. Since then, new data have emerged suggesting not only an increase in maternal fecundity but also larger paternal family sizes for homosexuals. These results are partly conflicting and indicate the need for a replication on a wider sample with a larger geographic distribution. This study examined the family trees of 250 male probands, of which 152 were homosexuals. The results confirmed the study of Camperio Ciani et al. (2004). We observed a significant fecundity increase even in primiparous mothers, which was not evident in the previous study. No evidence of increased paternal fecundity was found; thus, our data confirmed a sexually antagonistic inheritance partly linked to the X-chromosome that promotes fecundity in females and a homosexual sexual orientation in males.

Quelle: New evidence of genetic factors influencing sexual orientation in men: female fecundity increase in the maternal line

Ein grober Zusammenhang wäre sicherlich, dass Hormone sowohl die Fruchtbarkeit erhöhen als auch die sexuelle Identität prägen (pränatal im Mutterleib). Möglicherweise ergeben sich über eine Erhöhung des Östrogenspiegels und/oder ein Absenken des Testosteronspiegels fruchbarere Töchter, allerdings eben mit dem „Nachteil“ einer höheren Wahrscheinlichkeit homosexueller Söhne (Nachteil aus der Sicht der Gene, die sich über Homosexuelle eben schwerer vermehren können, ohne damit eine Wertung zu beabsichtigen).