The Genetics of Bisexuality (3/1/2007)

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A new genetic population model indicates that if a gene exists for homosexual behavior, that it would rapidly spread in populations. The same model also predicts widespread bisexuality.

In a new paper titled "Genetics and Bisexuality" published in the journal Nature by Dr. Vincent Savolainen and Laurent Lehmann, they examine recent work in genetics involving the possibility that a homosexual gene exists.

Though no gene for homosexual behavior has been found, evidence has been identified to suggest one does exist. For example, twins are more likely to both be gay compared to non-identical siblings. Also, male homosexuality is more often inherited from the mother.

Unlike heterosexuals, who dedicate a significant amount of time to reproductive sex, homosexuals are involved in non-reproductive sex, hampering the direct transmission of any gene that may be linked to homosexuality.

Their are three overall mechanisms that have been suggested in which varieties of homosexual genes could be maintained in a population: overdominance, sexual antagonistic selection, and kin altruism.

Overdominance

Overdominance would result in homosexual behavior in an individual who received the supposed homosexual gene from both parents. In this theory, it's suggested, that the gene is maintained in the population because it may be involved in attracting the opposite sex or may offer a reproductive advantage.

Sexual Antagonistic Selection

In the theory of sexual antagonistic selection, the gay gene would result in a reproductive loss for males that would be unwilling to reproduce sexually, however it would be considered a bonus when applied to females, perhaps making them more sexually appealing.

Kin Altruism

In the third theory, kin altruism, homosexuals would spend more time helping their own family members, by not reproducing themselves, but instead helping their relatives raise children. In this case it helps the gay gene continue to be passed on through the family.

In the first two cases, Dr. Sergey Gavrilets and Dr. William Rice have formalized these theories and have shown, that in large populations, the gay gene could be maintained in the population indefinitely. The kin altruism hypothesis has yet to stand up to the same tests.

These population genetic models, work on the premise, that if a gay gene or gene's exist, they depend on how the gene is expressed. The gay gene will produce a variable degree of homosexual behavior, and would be interpreted as a proportion of time devoted to homosexual rather than reproductive sex. Additionally, while the gay gene isn't fully expressed, meaning the individual is fully homosexual, they could be considered bisexual.

Though this research is still in the early stages, it suggests several ways to test for a homosexual gene. Now the real work will need to be started, in which families with homosexuals will need to be genetically screened, and analyzed to determine if a gay gene or gene's exist.

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