REQUEST: In this post I do not refer to, nor do I encourage reference to, any ethical/moral/emotional aspects of homosexuality. So please don't start an pro/anti- LGBT campaign in the comments section.

Are mammals (other than humans) known to engage in homosexual activity of any sort?

From the way I see it, homosexual activities carry no evolutionary or reproductive benefit: No offspring produced, no continuation of species...hence pointless.

Yes, I get that the "need to mate and to produce and protect offspring" is hard-wired into every (normal) mammalian brain. If I've interpreted this correctly; intercourse is a fairly energy-expensive act so if there were no immediately clear "incentive" for mammals to mate they wouldn't mate at all, hence heralding the decline and eventual extinction of a species. Nature solved this conundrum by ensuring that the brain would perceive intercourse as highly pleasurable, thereby securing the necessary "incentive" for mammals to mate.

The only "flaw" here, is that simply stimulating the genitals is sufficient enough to elicit a sensation of pleasure. So there's no real need to go through all the trouble of finding a suitable animal of the opposite sex and "do it" to feel good. A sufficiently intelligent mammal would soon figure that out; so this opens up two more possibilities: 1) Masturbation and 2) Homosexuality. (Since this post's on Homosexuality, I'm only going to deal with the latter)

So, a mammal intelligent enough to figure this out would have three options before it : 1) Heterosexual activity, 2) Masturbation, 3) Homosexual activity; the last two options being a way to bypass Nature's original intent.

So before I continue, I want to make what I mean by "homosexuality" very clear:

a) A being that displays option 1) or both 1) and 2) is heterosexual.

b) A being that displays options 1) and 3) [and maybe 2) too] is bisexual.

c) A being that displays option 3) or both 3) and 2) is homosexual.

[Just to make it explicitly clear, a homosexual will always steer clear of option 1)]

So let me just put all of that together and re-phrase my question:

Q- Are there any known instances where a (non-human) mammal consciously avoids heterosexual acts and instead prefers to engage in homosexual activity

Personally, I find this doubtful, since the existence of homosexuality (among humans) is the unintended result of Human self-consciousness/intelligence, something that other mammals apparently lack.

HOWEVER: (Considering another possible reason for homosexuality)

If occurrence of homosexual tendencies is (also) due to, say, the stochastic, faulty "hard-wiring" of the human brain due to mutation or damage to neural tissue (I'm not sure if this really is one of the reasons for homosexuality), then it would seem plausible that other mammals could also be affected by this stochastic "fault" and thereby display homosexual tendencies.

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    $\begingroup$ Have you looked at the wikipedia article on homosexual behaviour in animals? $\endgroup$ – Remi.b Apr 19 '17 at 15:21
  • $\begingroup$ @Remi No, no I haven't ._. $\endgroup$ – paracetamol Apr 19 '17 at 15:23
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    $\begingroup$ Sentences like the last two options being a way to bypass Nature's original intent. seems at least partially opinion based. You might want to have a look at the post How can homosexuality evolve despite natural selection?. Note also that there is no such thing as intention in nature but I suppose it was only a way of speaking) $\endgroup$ – Remi.b Apr 19 '17 at 15:24
  • $\begingroup$ @Remi "...I suppose it was only a way of speaking" It was ;) $\endgroup$ – paracetamol Apr 19 '17 at 15:36
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    $\begingroup$ Since answers will deal with homosexuality, I just want to mention that masturbation is quite natural as well, even porcupines do it. there are several hypothesis about its function with varying levels of support. Most likely several are true. $\endgroup$ – John Apr 20 '17 at 20:13

Although intuitively it would seem unlikely that there could be an evolutionary advantage to homosexuality (other than some theories regarding population control), homosexual behavior has been clearly observed in a variety of birds, monkeys and apes, lions, dolphins, lizards, insects, and plenty more.

The case of the bonobo is particularly striking in that homosexuality and bisexuality are more common than heterosexuality. According to this Wikipedia article:

Bonobos, which have a matriarchal society, unusual among apes, are a fully bisexual species—both males and females engage in heterosexual and homosexual behavior, being noted for female–female homosexuality in particular. Roughly 60% of all bonobo sexual activity occurs between two or more females. While the homosexual bonding system in bonobos represents the highest frequency of homosexuality known in any species, homosexuality has been reported for all great apes (a group which includes humans), as well as a number of other primate species.

Although the complexity of sexuality likely points to the existence of multiple genes playing a role in sexual behavior and preference, at least one study$^1$ points to a single gene playing an important role in the sexual behavior, of female mice:

In this study, we generated mutant mice specifically lacking the FucM gene that encodes fucose mutarotase. The homo- and heterozygous mutant females exhibited deficits in sexual receptivity as demonstrated by a drop in lordosis score. Moreover, the mutants displayed masculine behaviors and preferences to female urine over male urine.

1) Male-like sexual behavior of female mouse lacking fucose mutarotase, Dongkyu Park, Dongwook Choi, Junghoon Lee, Dae-sik Lim and Chankyu Park, BMC Genetics201011:62, DOI: 10.1186/1471-2156-11-62

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    $\begingroup$ Regarding your first sentence: biology.stackexchange.com/a/7675/107 $\endgroup$ – kmm Apr 20 '17 at 13:29
  • $\begingroup$ @kmm , interesting studies cited, particularly the twin study. Too bad there isn't more understood about the why of it, as in why heterosexual relatives of homosexuals are more promiscuous. Something to do with a balance of hormones maybe. Pretty complex picture. Thx for the link. $\endgroup$ – airhuff Apr 20 '17 at 16:38

This reminded me of the rat overpopulation experiments from the 1960'sish, in a nutshell, if rats are allowed to overpopulate in a confined area, the males become stressed, violent and homosexual.

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    $\begingroup$ Whoa! That's something you don't hear everyday. Did the study suggest any reason for male homosexuality in this case? (I can't seem to think of any ) $\endgroup$ – paracetamol Apr 20 '17 at 14:22
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    $\begingroup$ I can't remember any, other than as a means of displaying dominance, it has been used by armchair scientists as an example of why overpopulation leads to depravity and the "sin" of homosexuality. But mainly it's been used to guide animal welfare standards (at least in lab animals). $\endgroup$ – Oliver Houston Apr 20 '17 at 14:27

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