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Do bisexuals have any evolutionary advantage over straights and gays? Bonobos exhibit bisexuality extensively. Why so?

akm
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    Welcome to Biology.SE. You should have a look at Is homosexuality an adaptation in humans? and How can homosexuality evolve despite natural selection?. If insights from these posts don't answer your question, can you please elaborate on why they don't. – Remi.b Mar 02 '17 at 22:29
  • those questions are about homosexuality vs heterosexuality, mine is bisexuality vs homosexuality/heterosexuality. – akm Mar 02 '17 at 22:44
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    @AmitMaurya Can you point out what elements of the answers of those questions do not apply to your question? – Bryan Krause Mar 02 '17 at 22:53
  • @BryanKrause you tell me which element is applicable? is it established that bisexuality and homosexuality caused by same gene(s)? – akm Mar 02 '17 at 23:10
  • The genetic basis of either is not well established. The research cited also doesn't look at all at particular genes, it looks at reproductive rates among relatives. It also doesn't look at purely binary genders or sexual preferences and actually groups people into "heterosexuals" and "non-heterosexuals", the latter clearly including bisexuality. Please at least make an effort to read the answers and citations, like this one. – Bryan Krause Mar 02 '17 at 23:34
  • Also bonobo sexuality is interesting but I would be careful to overly anthropomorphize bonobos, despite their similarities to humans. It isn't right to consider bonobos bisexual without considering all of bonobo sexuality. Actions that humans interpret as sexual in bonobos are a major way that they interact with each other: you might as well ask why bonobos socialize with both sexes rather than why they interact sexually with both sexes. – Bryan Krause Mar 02 '17 at 23:38
  • so are you saying the behaviours observed in bonobos and interpreted as sexual by us may not be sexual at all for bonobos? – akm Mar 03 '17 at 11:07

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Like many things, whether bisexuality is advantageous for an individual's reproductive success or not depends on the environment. The fact that a wide variety of sexual systems and behavior exists in the animal kingdom suggests that. Also, "advantageous for an individual's reproductive success" doesn't necessarily imply "will spread via the processes of evolution"; for a trait to spread via natural selection+random mutation you need the trait to promote the individual's reproductive success, and for it to be reliably passed down to its offspring. And as the causes of sexual orientation in humans aren't well understood there is always the possibility it isn't strongly or genetically inherited.

As far as bonobos go, I am given to understand they use sex as a social tool, much more so than we do. In that context it does seem like bisexuality would be advantageous; it's silly to only be able to use your most powerful tool for conflict-resolution and social bonding on half of your community. This particular advantage won't be true, or will be much reduced, in species that don't use sex in the same way, i.e. all or most other species that we know of.

Oosaka
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  • are you saying bonobos' bisexuality is because of social learning rather than being genetically determined which is naturally selected? – akm Mar 03 '17 at 10:25
  • "Like many things, whether bisexuality is advantageous for an individual's reproductive success or not depends on the environment" so what environmental characteristics make bisexuality advantageous in bonobos but not other animals? – akm Mar 03 '17 at 10:38
  • @AmitMaurya I'm not saying that no; I don't know why Bonobos are bisexual. I certainly think it's plausible that bisexuality is subject to natural selection, and that it was naturally selected in Bonobos because of their social use of sex, but I don't know whether those things are true or not and I don't think research has demonstrated anything on the subject. – Oosaka Mar 03 '17 at 10:41
  • @AmitMaurya "so what environmental characteristics make bisexuality advantageous in bonobos but not other animals?" I described them in my answer; things like "other organisms of the species", "the social structure of a social species", etc are part of the environment. – Oosaka Mar 03 '17 at 10:42