Darwin's evolutionary model explains male homosexuality

Published in this week's issue of PLoS ONE, the Italian team including Andrea Camperio Ciani, Giovanni Zanzotto (of the University of Padova) and Paolo Cermelli of the University of Torino discovered that the origins of evolution and preservation of characteristics Male homosexuality in the human population can be explained by a model based on sex contrast selection in which the genetic factors replicate in the population by providing a reproductive advantage to a gender but again detrimental to other gender.

It is thought that male homosexuality is influenced by the physiological and social factors as well as the genetic component. This idea arises from the high relevance of sexual orientation in identical twins and male homosexuality occurs more commonly in men of the gay mother line. But female homosexuality does not suffer from such effects, indicating that these two phenomena have different origins and motivations.

It is difficult to explain male homosexuality by Darwin's evolutionary model due to the gene transport factor that leads to male homosexuality lower than average. This means that alleles affecting homosexuality will gradually disappear from the population. This changed when previous research by Camperio Ciani and colleagues published in 2004 found that women of the gay mother line had higher fertility than average.

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Given the challenges that all data posed, the authors of the new study published in PLoS ONE have considered many different theories about the phenomenon of diffusion of male homosexual genes. Hypothesis includes: maternal genetic effects on sons, superiority of heterozygous (found in malaria tolerance), and selection of sex contrast. The last hypothesis is a special aspect in Darwin's theory of evolution, in which genetic agents diffuse in the population by creating an advantage for one gender while bringing disadvantage to the other. This type of evolution was previously discovered in insects, birds and some mammals but has never been known in humans.

In order to explore and clarify the dynamics of genetic factors to form homosexuality, researchers must check the number of large models and eliminate them one by one. They concluded that the only potential model is the selection of sex contrast. Other models do not match the actual information, they all imply that the alleles will be extinct too easily or penetrate the population or cannot describe the male homosexual distribution model as well as the ability to reproduction of women in gay families.

The results of the sex contrast selection model show that the relationship between male homosexuality and female fertility increases in the population with a complex motive to maintain gay characteristics. Male sex at a relatively low but stable frequency, while emphasizing the effectiveness of heredity in the maternal line.

The results bring new information about male homosexuality. In particular, it changes the view of homosexuality as a disadvantage (it reduces male fertility), but we should consider the problem with a wider evolutionary framework with benefits. Specific genetic benefits, enhancing fertility for women. This may also be the evolutionary origin of this genetic trait in humans.

The widespread occurrence of sex contrast traits in evolutionary processes brings a reproductive advantage to one gender but is detrimental to the other only recently considered. This is considered the key mechanism through which high genetic variation rates are maintained in biological populations. Male homosexuality is just the first example of many other unknown gender contrast traits that contribute to the maintenance of natural genetic variability in humans. The new perspective that research models developed to study sex contrast selection can also bring a deeper understanding of the largest gender disagreements in the human population genetically. Our understanding of them is poor.

An unexpected significance of the new models is the impact of the sex contrast genetic factors of male homosexuality on the general reproductive power of a population. Research results show that the rate of gay men is a signal of the proportion of women with higher fertility. Therefore, the above genetic factors contribute to increasing the reproductive performance of the whole population compared to populations where these factors are less or less present. The rate of increase is greater when the reproductive power of the population decreases. This means that the gene that causes male homosexuality actually plays the role of a shock absorber spring for any external factor that reduces the overall fertility of a whole population.

Quote: Camperio Ciani A, Cermelli P, Zanzotto G (2008) Sexually Antagonistic Selection in Human Male Homosexuality (Selective sex contrast for male homosexuality). PLoS ONE 3 (6): e2282. doi: 10.1371 / journal.pone.0002282