Genetic Factors Increase Fecundity in Female Maternal Relatives
of Bisexual Men as in Homosexuals

Ciani AC, Iemmola F, Blecher SR.
University of Padova,
General Psychology,
Padova, Italy.
J Sex Med. 2008 Jul 15.


Introduction. 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. Aim. 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. Main Outcome Measures. Subjects completed a questionnaire on their sexual orientation, sexual behavior, and their own and their relatives' fecundity. Methods. 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. Results. 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. Conclusions. We present evidence of an X-chromosomal genetic factor that is associated with bisexuality in men and promotes fecundity in female carriers.
Private eugenics
'Designer babies'
Personal genomics
Genetic enhancement
Ashkenazi intelligence
Eugenics before Galton
Scandanavian eugenics
The literature of eugenics
Human self-domestication
Germline genetic engineering
Preimplantation genetic diagnosis
A life without pain? Hedonists take note'
Francis Galton and contemporary eugenics
Gene therapy and performance enhancement
Fecundity increase in the maternal line of gay men
Biological and psychosocial basis of sexual orientation
Sexually antagonistic selection in human male homosexuality

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