How does evolution explain homosexuality? (Kingdom, celibacy, blood, experience)

[tomspug]

This one makes no sense to me. Why is it that there are any homosexual tendencies in ANY species? Where do those instincts come from and why were they not weeded out by natural selection?

[angellous_evangellous]

I would suggest that homosexuality is a phenomenon which does not require homosexual parents in any species. Furthermore, the homosexual offspring may reproduce anyway. Therefore, the strong reproduce and yeild some homosexual offspring who may or may not reproduce.

I don't see why this would puzzle you.

[Gaddock]

Because:

1) Homosexuality isn't a (wholy) genetically determined trait. It is as much to do with early childhood experience and a range of other psychological factors(e.g. the more older brothers a male has, the more likely they are to be homosexual). Therefore there is no reason why this should be genetically excluded.

2) The distinction of homosexuality as an exclusive sexual preference is a relatively modern invention. At many points in history homosexual relationships have gone along side heterosexual ones for the same person. Many people historically have married to breed and still had sexual relationships with others (including same sex others) as well. We see this in the non-human animal kingdom too with some animals having both homosexual and heterosexual encounters.

3) Even a genetic disposition to homosexuality does not have to be passed on directly. It can be passed on as a dormant genetic tendancy for a number of generations without being active (and even then its only a tendancy, not a determinant).

Regards

Gaddock

[Sunstone]

So far as I know, this has only begun to be researched in the scientific community and there is as yet no consensus position.

[Willamena]

Originally Posted by tomspug

Where do those instincts come from and why were they not weeded out by natural selection?

That they are not "weeded out" or passed on from generation to generation suggests that they are not genetic.

I suspect they stem from love.

[MidnightBlue]

1) Why do heterosexual men have sex with women who are already pregnant and with women who are post-menopausal? Humans (and other animals) have engage in all kinds of non-reproductive sex, homosexual sex is just one of them.

2) Homosexuals do reproduce. Until fairly recently, probably most homosexuals reproduced. There are a lot of people alive today who would be surprised to know what I know about their grandfathers, and I know a lot of gay men and lesbians my age and younger who have biological children, too. Whenever there's pressure to conform to the expectations of a heterosexist society, a lot of people will marry someone of the opposite sex whether they really want to or not. My husband grew up in a religious family in a rural area, and married a woman because he didn't even know he had the option of being with a man. Even when people manage to accept their sexuality and form a healthy relationship, a lot of them just want children, just as a lot of heterosexuals do, and will manage to have children even if they don't want their primary relationship to be with the other biological parent. The children of homosexuals are also less likely to be a "surprise," and might, like the planned and wanted children of heterosexuals, have some advantage over children who are unplanned or unwanted or whose birth stigmatizes the mother.

3) Homosexuality may have some reproductive value even when homosexuals don't reproduce, in that homosexuals may devote greater resources to their nieces and nephews, who, after all, carry the genes of the homosexual's parents. Particularly when life expectancy was lower and death in childbirth was common, there may have been a strong advantage in having an uncle or aunt who didn't have children of his or her own to worry about. Families may also have benefited from alliances with other families as a result of homosexual relationships, just as they have always benefited similarly from heterosexual relationships. Celibacy has similar advantages; in medieval Europe it was often advantageous to have an uncle who was a Catholic clergyman, and in the Ottoman Empire it was sometimes advantageous to have an uncle who was a Janissary. So even when homosexuals and celibates don't themselves reproduce, they may help to pass on the genes of their parents.

4) Evolution doesn't imply that everything we do, and all our characteristics, are geared to survival and reproduction. It's not necessary that stamp collecting have any reproductive value; all that's necessary is that the genes of the stamp collector are perpetuated.

[9-10ths_Penguin]

MidnightBlue already covered some of this while I was typing, but here it is anyhow...

Originally Posted by tomspug

This one makes no sense to me. Why is it that there are any homosexual tendencies in ANY species? Where do those instincts come from and why were they not weeded out by natural selection?

Kin altruism seems to me to be the most plausible explanation. Here's the short version:

- an animal shares 50% of his or her genes with each child - a parent and a child have 50% of their genes in common.
- an animal also shares genes with other blood relatives: for instance, on average, siblings have 50% of their genes in common, and cousins share 12.5%.
- genes don't care which "container" they're in. In terms of propagating genes to the next generation, it makes no evolutionary difference whether some gene that you have is passed down through your own child or someone else's child - depending on the fitness of the child, but not on your personal relationship to him or her, the gene will hopefully continue and increase in frequency.

Based on all this, we have two strategies that might yield some evolutionary success:

1. Devote your effort and energy to protecting and benefiting a small number of family members with a high genetic similarity to you... i.e. the "standard" family where the parents (who both share 50% of DNA with each child) focus most of their energy on their own children.

2. Devote your effort and energy to protecting and benefiting a large number of family members with a lower, but still siginificant, genetic similarity to you... i.e. being part of the village (or, rather, extended family) that it takes to raise a child: taking part in the rearing of and providing for nieces/nephews, cousins, etc.

The most extreme example of this in nature are things like bee colonies: the whole hive is related, so it's in the evolutionary interest of the worker bees to support the queen, because that's the workers' own means of ensuring that their DNA gets passed to the next generation.

As long as there are some members of the family doing the actual procreating, other non-breeding family members can use that offspring as a way to pass their own DNA.

[angellous_evangellous]

Originally Posted by Gaddock

2) The distinction of homosexuality as an exclusive sexual preference is a relatively modern invention.
Gaddock

You consider Plato to be modern?

[9-10ths_Penguin]

Originally Posted by MidnightBlue