Saturday, December 09, 2006
Although biologists are still far from answering this question, scattered evidence for a possible gene influencing sexual orientation has recently encouraged scientists to map out a guide to future research. Because many possibilities for such a gene exist, scientists Sergey Gavrilets (homepage) and William Rice (homepage) have recently developed some theoretical guidelines and testable predictions for explaining the evolutionary causes of homosexuality.
"During the 1990s there was a short surge of interest by a small number of labs in finding major genes that might mediate homosexuality," Rice told PhysOrg.com. "However, for a variety of reasons, this effort waned by the turn of the century. I think that - when studying humans - many people shy away from studying sexual phenotypes in general and homosexuality in particular. Much of Sergey's and my motivation in writing our paper was to rekindle an interest in studying the genetic basis of homosexuality. I personally think that if a firm genetic foundation for homosexuality in humans were established, then many people would view this fascinating human phenotype more objectively."
During the past several decades, scientists have discovered some interesting patterns that may point toward genetic causes of homosexuality. Among the findings is that male homosexuality appears to be inherited more often from the mother than the father (Pillard). Also, natural selection might maintain a gene that may decrease the fecundity of one sex because the same gene also increases the fecundity of the other sex. In fact, recent data shows that female maternal relatives of gay men have higher than average reproduction capacity (Camperio-Ciani*). [Evolution]
Continued at "Is there a homosexuality gene?"
Based on "Genetic models of homosexuality: generating testable predictions" Proceedings of the Royal Society London B 273: 3031-3038
Homosexuality is a common occurrence in humans and other species, yet its genetic and evolutionary basis is poorly understood. Here, we formulate and study a series of simple mathematical models for the purpose of predicting empirical patterns that can be used to determine the form of selection that leads to polymorphism of genes influencing homosexuality. Specifically, we develop theory to make contrasting predictions about the genetic characteristics of genes influencing homosexuality including: (i) chromosomal location, (ii) dominance among segregating alleles and (iii) effect sizes that distinguish between the two major models for their polymorphism: the overdominance and sexual antagonism models. We conclude that the measurement of the genetic characteristics of quantitative trait loci (QTLs) found in genomic screens for genes influencing homosexuality can be highly informative in resolving the form of natural selection maintaining their polymorphism.
Full Text (PDF)
* Re Camperio-Ciani - See "Mother's genetics could influence sexual orientation" by Michael Hopkin (Nature reporter, London):
October 12, 2004
Genes could increase male homosexuality while boosting female reproduction.
A survey of Italian men has provided evidence that homosexuality may be partly influenced by genetics. The same genes that are proposed to predispose to homosexuality may also boost reproduction in women, solving the apparent paradox of why these genes have not been removed by natural selection.
By quizzing around 200 men of different sexual orientations, researchers at the University of Padua have discovered that maternal relatives of homosexual men tend to produce more offspring than those of heterosexuals. This suggests that the mothers and maternal aunts of homosexuals have a genetic advantage - but one that reduces reproduction when passed to male offspring.
"For a long time it has been a paradox," says Andrea Camperio-Ciani (homepage), who led the study. "But we have found that there might be a set of genes that, in males, influences homosexuality but in females increases fecundity." (Continued at above link).
An earlier post "Homosexuality: Gay animals come out of the closet?"
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