If Evolution is true, why are there homosexuals?

That question has been asked about homosexuality and evolution since evolution was first proposed. Scientists ask because they're curious to know the answer. Creationists and anti-evolutionists ask because they think if they can get evolution thrown out, they'll win the argument by default.

But it remains a valid question.

Natural selection tends to weed out traits that hinder survival, and favor traits that promote survival. But it's not always that simple.

Sickle-cell anemia, for example, is endemic in West Africa. You'd think this genetic illness would be eliminated very quickly from the gene pool. At most, you'd see it at a very low level, corresponding to the interval between when it spontaneously arises in the population and when it's selected out.

In fact, it's found at very high levels.

The reason it's found at high levels is that people who carry one copy of the gene for sickle cell anemia don't show symptoms (or at least very few symptoms) of the disease, but their blood cells don't support the growth of malarial parasites. Being a carrier for sickle cell anemia protects a person from malaria.

You can even calculate the chance of leaving behind offspring given the odds of dying from malaria versus the odds of dying from sickle-cell anemia, and find the level of occurrence of sickle-cell anemia that corresponds to a population where the maximum possible number of children survive to bear children themselves.

This number is known as the Hardy-Weinberg Equilibrium, and the good match between the frequencies of detremental genes and calculated fitness values is one of the bits of evidence supporting Darwin's ideas.

Homosexuality seems to have at least some genetic component. At the very least, there has been no apparent need to develop genetic mechanisms that would absolutely preclude its occurrance. Given that homosexuality occurs, there are a few possibilities:

1. Homosexuality itself confers some benefit toward propagating the species.
2. Homosexuality is a side-effect of a gene that confers a benefit elsewhere.
3. Evolution is disproven, we were all created, and the Creator deemed it good that homosexuality occur at some low level in the population.
4. Other reasons not listed above

The Herald Sun presents this article suggesting that homosexuality in men is correlated with higher fertility in women. In other words, a gene that tends to keep men who carry it from reproducing makes women who carry it more fertile. At low levels, the increase in birthrate in woman carriers will more than balance out the loss in birthrate from men who are less inclined to reproduce.

This study is described as "controversial", of course. If it stands up, though, it would explain at least a few things.