This is another copy of something I wrote on another forum, with a few additions:
A common argument I see against homosexuality being natural is that if homosexuality was a genetic trait it would be wiped out because those who hold that trait would not reproduce. The problem with this “it couldn’t be passed on” argument is it assumes that there is some gene that automatically make someone homosexual, and that people either have the gene or they don’t and that makes them homosexual or not. Their could be genes in human beings that create conditions where homosexuality will appear in a small number of people who have those genes, and those genes could be universal. How that randomness is created could have something to do with the child in development or any of a number of things, perhaps it is triggered by some relatively unlikely development while the child is growing in the woom. Other traits follow this pattern of a small probability of something happening within humans that is hard-wired but not determined directly by inheritance, for example left handedness vs. right handedness.
If the traits that lead to potential homosexuality are beneficial in other ways (very likely since they have to do with sexuality which is extremely important as far as an animal reproducing) then it would be passed on even though the potential for homosexuality would hurt the species. The negative impact of a small number being homosexual could have been outweighed by the positive benefits to the community.