[T Ruth]

1. I am not sure I follow this point. To the extent I understand it, I think that darwinists would say that any gene or combination of genes which confers a competitive disadvantage will over time inexorably lose the competition for survival, and cease to be replicated. The real game for a comitted darwinist who wants to show a genetic basis for homosexuality would be to show that homosexuality confers a competitive advantage(!). Otherwise, it would be merely a genetic "disease," like, e.g., Gaucher disease, which under the operation of natural selection must eventually disappear; not to mention that calling homosexuality a genetic disease would be politically incorrect.

2. Homosexuality may be a behavioral adaptation to overcrowding, but it is obviously not a necessary adaptation.

[Ostlandr]

I'm not particularly a Darwinist, but the way I learned it in school, each individual has a unique genetic makeup. Sometimes, this genetic pattern results in a fatal genetic disease; sometimes it results in an adaptation that provides a competitive advantage. Wether or not it is an advantage depends on environment; hence, Northern Europeans evolved with light skin (produces more vitamin D in low light conditions) extra body hair (for the cold) and they retain the ability to digest milk as adults;
Africans evolved darker skin (for UV protection.)
I kind of fall in the middle on the whole creation/evolution debate; I tend to think that God set the works of Creation in motion, and now just sits back and adjusts the machinery from time to time.