Evolution doesn't explain homosexuality

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Claim

Evolution doesn't explain homosexuality. Traits evolve due to greater reproductive success, and homosexuals aren't big on reproduction.

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Responses

  1. The lack of a validated evolutionary explanation for one particular trait or behaviour is no counterballance to the vast weight of evidence in the theory's favour.
  2. Evolution does not need to explain all traits as adaptations, because there are a number of constraints on what evolution can do:
    1. Evolution requires that variation in a trait is heritable. It is possible that sexual orientation is not heritable, in which case it would be unrelated to biological evolution.
    2. Evolution requires that variation in a trait affects reproductive rates. Thus, homosexual behavior would only be maladaptive if it directly prevents or impairs reproductive heterosexual behavior, or interferes with child-rearing. Many animal species that display homosexual behavior reproduce quite happily, just as many humans with homosexual preferences have sired/mothered children (or may "change preferences" over time, or simply be bisexual). Simplistic definitions of behavior do not lend themselves well to discussing the complexities of sexual behavior.
    3. Traits are not independent of each other. Although no links are known for homosexuality, evolutionarily maladaptive traits may evolve if they are linked to traits that are more adaptive (e.g. cystic fibrosis is linked to immunity to cholera).
    4. Evolution has a time lag. There have been vast revolutions in the human environment (societal organisation and culture) in, from the point of view of evolution, a very small time scale. Thus, humans will express many traits and behaviours as a result of their current societal or cultural situation over which evolution has not yet been able to act.
  3. Creationism has an even more difficult time explaining homosexuality. "The devil did it" is not a meaningful explanation.
  4. While there is no proven explanation for how homosexuality could be selected for (or, at least, not selected against), there are several plausible possibilities as to why it could persist or even be selected for in populations (see also, the gay gene):
    1. It can be explained through mathematical models of inclusive fitness. Since you and your siblings share 1/2 of your genes, that's the same as your children. If your sibling could have twice as many children as you could--if you were able to devote more time to raising them until maturity--then genetically, they would be indifferent. A person who is seeking to ensure the success of children already alive can be equally as successful genetically as one who seeks to have more children. It is merely an extension of the choice between parental investment and fecundity.
    2. A gene may exist that causes women to have a heightened desire for men. This gene may also predispose men to homosexuality.
    3. Homosexual and bisexual men may gain from having strong male friends who will help and defend them and their families when there is a threat. Likewise, lesbian and bisexual women also have close women friends who can help them and their families. Perhaps male homosexsuality is more common than lesbianism. Perhaps a strong male friend is potentially more helpful.
    4. Male giraffes mount each other in order to reaffirm their social standings in the herd in a non-aggressive manner; our close relatives, Bonobo Chimpanzees, similarly use sexual acts for non-reproductive purposes. Bonobos also use sex to reaffirm social bonds in heterosexual and homosexual contexts.
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