@Diest TKO,
I heard somebody asking for an evolutionary explanation for homosexuality, so I am here to provide.
The mistake that most people make when thinking about evolution is that it occurs at the level of the individual organism. It doesn't. It occurs at the level of the gene. And sometimes it is beneficial for a gene to sacrifice the organism to save other genes.
This is a drastically oversimplified example, but it gets the point of cross. Imagine that homosexuality is controlled by a single, recessive gene, so you need two copies to be a homosexual. If you only get one, you are straight. A homosexual then, would be relatively rare in the population, but could survive without reproducing themselves. Instead, they would contribute to the survival odds of the gene in those around them, who only carry a single copy of the gene, thus increasing the odds that they survive and successfully reproduce. As long as they are able to do this for 3 individuals, it actually does better than if they just took care of themselves, because 3 copies of the gene are being cared for instead of just two, and three individuals with the gene are reproducing the gene in their offspring instead of just the one.
Again, this is a drastic oversimplification, but it's useful nonetheless, and should clear up how such a genetic predisposition could propogate.