Homosexual selection: The power of same-sex liaisons

[n2doc]

07 December 2009 by Kate Douglas


Homosexual encounter. Female Laysan albatrosses on the Hawaiian island of Oahu pair off with other females. (Image: Tui De Roy/Minden Pictures/FLPA)

NOT long ago, the news was full of reports about two male Humboldt penguins at a zoo in Germany that adopted an egg, hatched it and reared the chick together. It seems like every time you turn around, the media spotlight has fallen on another example of same-sex liaisons in the animal kingdom.

In the past few years, the ubiquity of such behaviour has become apparent. This summer evolutionary biologists Marlene Zuk and Nathan Bailey from the University of California, Riverside, published a paper on the subject that included examples from dozens of species ranging from dung flies and woodpeckers to bison and macaques.

That is just the beginning of the story. The burning question is why same-sex behaviour would evolve at all when it runs counter to evolutionary principles. But does it? In fact there are many good reasons for same-sex sexual behaviour. What's more, Zuk and Bailey suggest that in a species where it is common, it is an important driving force in evolution.

Although terms such as homosexual, gay and transgender are commonly used by the mass media, and even by some ethologists, Bailey and Zuk believe you shouldn't extend these descriptors of human sexuality to animals. "It's not simply that they are burdened with the weight of social, moral and political implications, which can obscure objective scientific study," says Bailey. "The problem is that while we can observe the sexual behaviour of animals, we often have little inkling about what motivates it." Besides, as far as we know animals do not form sexual self-identities in the way humans do, he adds. That is why he and Zuk prefer to use the more objective term "same-sex sexual behaviour", which they define as behaviours found in two animals of the same sex that you would find in opposite-sex pairs during courtship, copulation or parenting.

much more:
http://www.newscientist.com/article/mg20427370.800-homosexual-selection-the-power-of-samesex-liaisons.html

[Hekate]

1. KnR. Fascinating. I can think of a couple of evolutionary advantages to same-sex pairing...

Thanks for the interesting post, n2doc.

Hekate

[TlalocW]

2. I can easily explain homosexual behavior in animals

As I was "lucky" enough to have it explained to me by an evangelist visiting my campus when I was in college.

God gave man dominion over the Earth and all animals on it, but man's sin covers the Earth so even though animals have no souls that can be stained with sin, man's sinful nature still influences them.

Now you know.

TlalocW

[BrklynLiberal]

4. Ooooooooh. I see...

:silly: :crazy: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

[TZ]

3. Interesting, but not particularly new

I learned about about this behavior in ecology in college in 1989. In populations that are near carrying capacity in an ecosystem, behavior that slows reproductive behavior is going to be seen.
This is why when I hear the fundies going on about homosexuality being "unnatural" I want to slap them. Its very natural.

[BrklynLiberal]

5. What about the theory that it may be a response to over-population, and

may be Mother Nature's own form of population control?

[TZ]

10. Yes.

In populations near carrying capacity (the maximum number of individuals an ecosystem can sustain) behavior that reduces population is selected for...same sex mating behavior being one of them.

[hunter]

6. It seems to me those explanations are too complicated.

The genes governing sexual attraction needn't be sex linked.

To put it in human terms, imagine a non-sex linked gene that increases one's sexual attraction to males. In a woman it's the kind of attraction that increases the likelihood of the farmer's daughter climbing out the window at night for a secret liaison with her forbidden boyfriend or incites Rapunzul to let her hair down for her Prince.

In a male this same gene strengthens social ties with other males, and in the situations where the sex linked attractions are not as strong, increases the propensity for homosexual behaviors.

Of course it's not that simple because there are a large number of genes related to sexuality, but in this very simple model a "gay gene" can increase the odds that an individual will survive and reproduce.

[Zodiak]

7. Kin selection

It is the idea that a non-reproductive member of a community can contribute to the community's overall fitness by taking care of the offspring of others in the group. That individual is making their genes more likely to pass down even if they are not the ones passing it down themselves.

Kin selection is why there are worker bees and ants.

The only way for kin selection to occur in a group of animals with an alpha male social system is for the beta males to adopt behaviors that tells the alpha male that they are not in competition for mates. Homosexuality would be one of those behaviors.

[BadgerKid]

8. Interesting point. What about both-sex behavior?

What if the alpha male got killed or died, would it be reasonable that the previously subordinate homosexual-displaying males to "become" heterosexual to compete for dominance and mating rights amidst the power vacuum? If so, it suggests some animals have the potential to exhibit a spectrum of sexual behavior that depends in part on external factors.

For the record, I support gay et al. rights. I was curious about more info about the animal world that is free of human culture.

[Zodiak]

9. I am not a primatologist or a mammalogist

I am an entomologist, so I cannot give you an answer with sufficient detail.

I apologize.

However, if I were to speculate, I would say that the "new" alpha male would be a previously ousted beta who lost a competition with the alpha in the past, or a younger one that has not adopted a more feminized affect yet. Previously feminized males could make very poor alphas, and would probably be supplanted in short order....and probably by some alpha outside the group who has no compunction about killing whom he challenges (which goes against the principle of kin selection)!

Also, homosexual behavior does not just occur in alpha-male based social systems. Chimps are that way, and so I thought it pertinent since they are our closest living relatives.

[TZ]

11. I've studied kin selection extensively

That explains non reproductive behavior (like cooperative brooding) by individuals that aren't likely to reproduce--not active drives . It however does NOT explain same sex mating behavior...that is more tied to population in an ecosystem. Birds have been one of the more common type of animals to expresse same sex behavior, but they do not normally stay in large groups of related individuals.

[Zodiak]

12. No, it does not explain the behavior

My other explanation does (about social bonds with the group being stronger if the alpha male doesn't see the male in question as a threat). So the behavior makes it more likely that the group will benefit from kin selection.

But I do believe that kin selection is what fixes the behavior into a population.

Here are the two current hypotheses in a nutshell:

"Briefly, the former hypothesis supposes that phenotypic homosexuality is the result of homozygosity for recessive 'homosexual' genes. If a heterozygote, possessing one 'homosexual' genetic allele and one 'heterosexual' allele, is phenotypically heterosexual, and more reproductive than an individual who is homozygotic for the 'heterosexual' alleles, then the heterozygotic combination will be preferentially selected in future generations. In this way, the 'homosexual' genes are preserved. This explanation may seem implausible; for one thing, it hardly seems likely that only a single, major gene is involved in determining sexual preference However, various genetic concepts (incomplete penetrance, epistasis, etc.) may be utilised to expand the hypothesis (e.g. Klintworth 1962, Fuller & Thompson 1978).

The key to the kin selection hypothesis is that it does not matter how one's genes are passed to the next generation, as long as they are. Siblings share, on average, 50% of their genes. Therefore, if an individual shows altruistic behaviour towards its siblings which results in an increased likelihood of the siblings leaving or raising offspring, then that individual is, in effect, favouring its own success. Although it is hard to see how such a process could operate in modern society, sociobiology concerns itself with how behavioural traits have evolved and been selected from primitive societies to the present day. It has been suggested that, in primitive societies, homosexuals may have formed a 'sterile caste' which could devote itself to helping mothers to rear their young.

Sociobiological explanations of homosexuality are recent and very speculative, and are currently intended only to highlight the possibility of genetic transmission of such a trait. Much more research is required before these hypotheses can develop into credible scientific theories. "


The reason I think the kin selection hypothesis holds true for early humans is a study done on Pacific Islanders where there is a "homosexual caste" of males that have sex with straight men in the group and help extensively with raising nephews and nieces. This is some of the first support for the kin selection hypothesis. Western culture did not produce such data because basically Christianity fucked up the free development of social norms. But it is there.

[marginlized]

13. For Further Reading

Ok, for further reading there is Bruce Bagemihl's "Biological Exuberance" in which he collects and reviews the data on nearly 300 species of mammals and birds. He shows that homosexual behavior has been observed in nearly 1500 species and well documented in 500.

This broad biological evidence alone indicates that whatever the cause(s), they are certainly deeper in our genetic past than any observations in modern man, and certainly more complex than simple explanations of altruistic day care.

Wikipedia offers this:

The authors of a 2008 study stated that "there is considerable evidence that human sexual orientation is genetically influenced, so it is not known how homosexuality, which tends to lower reproductive success, is maintained in the population at a relatively high frequency". They hypothesized that "while genes predisposing to homosexuality reduce homosexuals' reproductive success, they may confer some advantage in heterosexuals who carry them". Their results suggested that "genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population".<84> A 2009 study also suggested a significant increase in fecundity in the females related to the homosexual people from the maternal line (but not in those related from the paternal one).

To paraphrase Haldane, the Universe is not only queerer than you imagine, it is queerer than you can imagine.