I recently had this quick debate with someone on a message board I frequent. I would like to point out that the person I debated isn't someone I'd consider homophobic. In fact she is quite committed to gay rights. Her comment came off as much as anything else like an intellectual inquiry. None the less, I wanted to share this because the question as to the evolutionary purpose of homosexuality often comes up. Unlike many who facetiously ask this question, my debate opponent here actually believes in evolution. This wasn't a hostile debate.
So without further ado, here is our exchange (slightly edited for clarification).
As wonderful as you may be, you are of no use to me if I'm "Mother Nature" unless homosexuality in nature is a form of population control. I've never seen any statistical evidence that indicates that. The incidence of homosexuality seems to be consistent in densely populated areas as well as sparsely populated areas. If anyone has any data to the contrary, I would be super interested in reading it.
There are two assumptions you make that are faulty.
First of all you make the assumption that all variations in a species result from evolutionary need. The theory of evolution rests on the concept of natural selection not need. Many traits are selected that aren't necessarily useful. As has been pointed out, the selection of various eye colors is not about need. So, need isn't necessarily the reason a trait is selected.
When need is the reason for selection it is about survivability. That is to say, what traits aid in survival of the next generation. In one context, the trait may be physical abilities. In another context, it might be intellectual abilities.
The second faulty assumption is that the only possible advantage of homosexuality would be population control.
There is, as it turns out, more than one way to skin a cat. That is to say, there are more ways to assure the survivability of your children than mating with the right man. Let's look at two families, one with no homosexual members, and one with a homosexual member.
In the first family all the siblings are heterosexual. There are five siblings. They each have a spouse. They each have children of their own. Let's presume there is the historical gender based division of labor in this family. The men hunt. The women gather and rear the children. So, one day the men go hunting boar. The five men go hunting and they each bring back one boar. The women each bring back a basket of berries and fruit. This is a successful day. All the men and women and all the children should be able to eat.
But what if it is a bad day hunting and gathering. What if the men only catch four boars and the women only collect four baskets of fruit and berries? Well, now they have to make four families worth of stretch through five families (the Republican solution is "he who does not catch a boar has to go hungry -- as well as his children." But that's for another debate).
So, as you see, in the all-heterosexual family, on sparse days, there is less to eat. If this happens enough, survivability of the family is reduced.
But what if there was a gay person in the family?
Then four siblings would have four spouses and four sets of children. The gay brother would have no children. On days when each male brought back a boar, because the gay brother has no children -- there would be an excess of meat. This meat could be turned to jerky and saved for a lean day. In this scenario, having a gay brother would increase the survivability of the family and the children. The family unit is, thus, strengthened due to the presence of a gay brother.
This also aids the gay brother. Since his siblings each share 50% of his genes, as he aids his family, his siblings can have more children, thus increasing the likelihood that his genetic material survives into the next generation.
Therefore, under these circumstances gay people don't necessarily aid to control the population. In fact, their presence in the family could free his siblings to reproduce even more.
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My debate opponent's response:
That's good analysis and an interesting line of thought. I like it because I've always had the gut feeling that homosexuality was somehow a real factor in the equation. I just don't know how.