New Evidence of Genetic Factors Influencing Sexual Orientation in Men: Female Fecundity Increase in the Maternal Line
by
Iemmola F, Camperio Ciani A.
Department of General Psychology (LIRIPAC),
University of Padova,
via Belzoni 80, 35121, Padova, Italy.
JArch Sex Behav. 2008 Jun 17.

ABSTRACT

There 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.

Biohappiness
Reprogenetics
Genospirituality
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
The evolution of sexual behaviour
A life without pain? Hedonists take note'
Francis Galton and contemporary eugenics
Gene therapy and performance enhancement
Biological and psychosocial basis of sexual orientation
Increased fecundity in female maternal relatives of bisexual men

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