What is the biological purpose of homosexuality?

That is factually incorrect. It depends on where you purchase it! :slight_smile:

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As mentioned it vary widely from time to time and place to place, but there were also rigid (no pun intended) guidelines. Anal penetration was not permissible between two men of equal social rank in Greece or in Rome- I’m sure it happened but it was as frowned upon as homosexuality in general was later and not something you’d be likely to confess. Fellatio was also discouraged. Dry humping (frottage), ‘between the thighs’ and mutual masturbation were more common since neither of these implied or imposed active/passive (read male/female) roles.
What a man did to another man of inferior social status- particularly a male prostitute (who earned less than women- the reverse is true today as a general rule) or a male slave- was likely not good water cooler conversation but it was his business and legal.

In some cultures eunuchs (who had many varieties- some had been completely emasculated, some had only the testicles removed) were considered a third gender altogether and were very popular sex toys when they were youthful and servants when they were no longer sexually desirable.
The Greco-Roman ideal for a male sex partner was what we’d call a twink with a big butt and small penis. (If you’re not familiar with the term pink, think Zac Efron or a young Leonardo DiCaprio- boyish, naturally hairless body, shaggy hair.)

Lesbianism existed in the ancient world of course but surprisingly little is written about it. There’s not even a clear condemnation of it in the Old Testament and only a vague condemnation of something that might include lesbianism in the Pauline “521 More Things That Get Me Pissed Off” writings. In Persian harems lesbianism between concubines and wives was considered acceptable, especially when the master was away, since it allowed them to get their release without infidelity; in some cultures women having sex with eunuchs, which was considered neither gay nor straight, was also permissible since many eunuchs are capable of sex (especially if they were testicular eunuchs only and that after the first signs of puberty) but not of impregnation. The castrati who began popping up in the Renaissance and continued until the late 18th century were actually sought after as lovers by the Renaissance set of their day since
1- no chance of pregnancy
2- testicular post-puberty eunuchs had the reputation of holding erections much longer than a “full” man
3- eunuchs were usually much more limber than “full” males (a side effect of their ‘operation’)
All eunuchs were forbidden to marry in pre or post Christian Europe even though they existed in huge numbers at times (though there might be a very few exceptions that required imperial or papal permission on the individual basis only and with extenuating circumstances). In western Europe they were also forbidden to join the military or become clergy, though in the Byzantine empire (where they were the nucleus of the civil service, kind of like the gay personal assistants of today) they could enter pretty much any profession. Narses was a famous eunuch general in Byzantium and there were many priests and occasional metropolitans (roughly equivalent to archbishop in Eastern Orthodox Christianity) who were eunuchs. They were barred from being emperor (and in fact many imperial bastards or men with a possible claim to the thrown were castrated to prevent their succession) but could hold high office and there were numerous eunuchs from antiquity to the late middle ages who served as the power behind the throne (Bagoas of Persia a generation before Alexander [not to be confused with Alex’s eunuch pal of the same name] and John the Orphanmaster of Constantinople [who ultimately arranged for his brother to become emperor in the 11th century] being two of the more famous).

Speaking of left handedness, a fact I think is interesting:

In sets of identical twins in which one is left-handed the other has about a 3 in 4 chance of being left handed. About a quarter of all pairs of identical twins have one who is left handed.

In studies of identical twins in which one identifies as gay the other has a 1 in 2 chance of identifying as gay. With fraternal twins it’s about 1 in 5 (slightly larger than the chance of any other sibling of a gay person has of being gay, but not significantly).

The twin studies imply that there are genetic and environmental components to both left handedness and homosexuality. The latter of course is more difficult to measure as it is largely dependent on the other person’s self identity and honesty, while left handedness is easier to independently identify.

Anecdotal only, but I’ve known two gay men and one lesbian who had identical twins and in all cases the twin was gay. The fraternal twins who played Tabitha on Bewitched were Erin Murphy (married three times and the mother of six children) and Diane Murphy (an out lesbian). I’m not sure if they were fraternal or identical as I’ve read both. This is them as childrenand this is them as adults(when they’re definitely not identical but that has much to do with outfits and hairstyles).

Japanese macaques exhibit female/female sexual matings. Each mating season, the macaques pair off and engage in courtships with various individuals. Sometimes the relationships are heterosexual, other times they are homosexual. There are some female Japanese macaques who only have homosexual relationships. The researcher who studied this group wrote a paper on it where he argued that the female/female relationships were just a by product of excess sexuality. Since the majority of female macaques who entered into lesbian relationships weren’t negatively affected by them, there was no need for evolution to weed it out. Even the selective pressure on the females who always engaged in same-sex relationship wasn’t enough to end the practice.

Capuchin monkeys have a lot of male/male sex. Tension runs high between non-related adult capuchin males since they tend to live with males who are not related to them and males can monopolize large groups of females. Forming bonds with non-related males is difficult and they have sex to cement these bonds. Males who are very good at forming bonds with non-related males would be much better at war and indeed, when we look at human societies, highly constructed male/male sexuality is often found in war cultures and amongst warriors. Since male/male bonding is encouraged at high levels, occasionally a male will be produced who prefers the company of men exclusively. This is rare and, since the majority of the males benefit from forming male/male bonds, there is not need for evolution to work against this property.

Amongst chimps, female/female sexual bonding only exists in artificial situations such as zoos since female chimps are in competition with each other for food in the wild. Yet, female chimps who only prefer to sexually chase after and mate with other females is known.

There are many reasons as to why homosexuality exists in nature.

Sampiro, sex is not rape for the majority of the animal kingdom. In fact, I would say that rape is the exception rather than the norm. The animal kingdom is wide and varied, but the females actively participate in mating and are very selective about partners in the majority of species I’ve come across.

Maybe it’s your cologne.:wink:

The answer may lie in the answer to another question…

Why do women continue to desire sex after menopause? Shouldn’t the sex drive go away after the ability to produce offspring is gone?

Sounds like the current human condition to me, other than the fact we allow certain people to starve while the rest of us become increasingly obese.

What is the evolutionary advantage of self-induced population control? Makes no sense to me. Natural selection works mainly, almost exclusively, on the individual level. Population control would only work on the group level.

And I agree with **chimera ** and disagree with **Sampiro **that “rape” does not account for the majority of sex in the animal kingdom. Unless he’s got a cite to back that tup.

I have a couple of points to consider. Please note that my points have to do with humans organized at a strictly tribal level - anything larger than that and the sociology will change greatly. However, I would hazard a guess that most of our evolution occurred at the tribal level.

Humans are essentially pack animals, like wolves (as opposed to solitary animals, like tigers or bears). This is a critical distinction, because it means that supporting the pack is essential to the survival of the individual members of the pack. Since every adult in the pack will share a greater percentage of DNA with all of the children than with individuals outside of the pack, even someone who doesn’t have children of his/her body still has a genetic stake in the children. So the selection pressure against homosexuality is not as overt as it seems at first glance. From this though, I would guess that the genes are recessive, so that they can pass through generations without completely disappearing.

One advantage I’ve considered has to do with a tendency for human cultures to make wives status symbols (especially more attractive wives). However, men and women have roles in the pack that have very little to do with procreation - hunting and war for men, gathering and childcare for women. If a small number of men of the tribe are homosexual, they are available for the hunting and war parties, but not competing with the other men for women’s sexual favors (and thus are less likely to start damaging fights) . Similarly, women who are lesbian or asexual may serve as status wives and help with the gathering and childcare while not competing with the co-wives for the husband’s sexual favors.

Another advantage I’ve thought about is a what I would call a bell curve quandary - that by changing part of the bell curve, you would be changing the whole spectrum. The quandary is then that if the factors that create homosexuality were eliminated from the gene pool, it could change the workings of human sexuality across the board and be detrimental to reproduction for the whole population.
One final thought. I’ve seen a study that showed that human’s (and other primates’) chances of having a male vs. female child was affected slightly (but in a statistically significant manner) by the mother’s status - women of lower status tend to have more female children, whereas women of higher status have more male children. The hypothesis was that women get their status from their mate, whereas men get their status from their mother, and that this would then optimize their children’s status. In another study that I’ve heard of, when a woman has many children, later children are more likely to be homosexual than earlier children. Because these later children would not be competing for their siblings’ status, they would then be able to support their siblings’ status and thus improve the survival of grandma’s grandchildren.
Did I say that was my final thought? Wait, I had one more. Because much of our post-tribal history (at least for christian culture, I can’t answer for other cultures) has had such powerful strictures against homosexual behavior, it’s quite possible that there are far more people with homosexual genes now than there were in tribal human cultures. It may be that our greater openness to homosexuality now will do more to reduce it than 6000 years of Leviticus.

Quoth Mozart1220:

Oh, that’s easy. Women desire sex before menopause because women who desire sex tend to have more offspring. And there’s very little benefit to abstaining from sex after menopause, so it’d be more trouble than it’s worth to evolve a mechanism to shut off that desire (especially since, if that mechanism malfunctioned, it could shut off desire early and thus reduce fecundity). In fact, even without reproduction, there are probably still benefits to sex after menopause, although minor compared with reproduction: An old woman can contribute to the success of her offspring in various ways (this is why we live past reproductive age in the first place), and a woman who has a strong relationship with her husband is probably better-equipped to do so. So sex, by maintaining that relationship, indirectly helps her genes.

Social bonding.

It’s rare they make a report. Rape is perhaps a word ill chosen, but it’s shorter than saying “the majority of sex in the animal kingdom is for the male an aggressive act undertaken with no real concern for the consent, comfort, physiological or psychological well being of the female, with no emotional or erotic motivation and solely to satisfy his own sexual urges”. Very few species have non-procreative sex or seem to have any kind of emotional connection before or after the congress.

I always knew there was something fishy about those birds…

Not sure I’d agree with that considering that there is far more invertebrate life than vertebrate. Seems like for most invertebrate reproduction, the male post-coitus is almost an afterthought, if not an after-dinner mint.

The advantage is that a population density beyond a certain point is deleterious to both the individual and the population in toto. I’m no expert in biological evolution, but it seems reasonable that a population of humans without an effective homeostatic population mechanism could easily grow to outstrip the resources of its environment, rendering them less fit (individually and en masse) than a population that does not grow beyond its sweet-spot density. If the less fit population thereafter competes with the more fit population, a higher percentage of the more fit population should survive to pass on the beneficial gene to succeeding generations—in this case, the homosexual homeostatic population control gene :D.

So, I see a clear advantage to having a self-induced population control mechanism.
The question is, can such a trait evolve in a group, and, if so, is there any evidence that it has?

Not really. Remember, natural selection acts primarily on the individual level. The better evolutionary strategy is to let the fittest survive, and let the less fit die of starvation.

If the majority of animal kingdom sex is rape, then why do so many males put on displays - plumage, dances, mating calls, etc. - to attract the attention of the female? Generally in the animal kingdom the males have a competition and the female chooses her mate from the most attractive. Very rarely is it forced.

Of course, often female reluctance in humans is shaped as much by social forces as by desire. (long-term vs. short term planning)

Many have drawn that inference also, and it sounds correct. However, mice are not= humans, so it may be wrong also.

I think the whole “Mice will kill the young and have gay sex” thing started when Minnie came home to find Mickey coked up, surrounded by her dead nephews and nieces and having sex with their friend Jerry. “It’s not me, it’s the size of the house… society’s to blame!” Two years of therapy, some appearances on Larry King and a book deal (Cramp Pains by M & M) later their marriage was reportedly doing better.

This is simply false and if you took some time to look at how sex is practiced amongst different orders and species, you would see this is true. For example, in the vast majority of bird species, rape is impossible. There are exceptions, such as ducks, but they are the minority. Amongst primates, I’ve only heard of rape with chimps. I’ve never seen a capuchin force another capuchin despite the fact that the majority of females are considerably smaller than the males and are bullied around by them in other ways.

For females to have no control over how males mate with them would be horrible for them and the species. For every male tactic to gain females, there are both external and internal tactics by females to avoid male coercion and to take control over both how she mates, with who she mates, and who gets to father her babies. Because of these strong female countermeasures, rape isn’t a good evolutionary strategy except in a few selection species. In the species where rape occurs, the females are currently evolving all sorts of countermeasures and, a lot of the time, they do have a manner of control over who impregnates them. For reading about cryptic sexual selection check out this excellent book. In most mating systems, the females are the ones who hold the most control, after all, they have the most to lose.

And again, amongst primates, most of the time, sex is not about procreation. It’s about forming bonds, making friends, and expressing interest in others. I’ve seen female capuchins sexually harass males who weren’t interested in them.