Homosexuality is an expected consequence of nature using sexual reproduction as a method of providing genetic diversity.
There would be little diversity resulting from all males being attracted to the same trait, and all females doing likewise. In the extreme case, not only would all males be attracted to the same type of female, they would be attracted to a single individual. This would frustrate the purpose of genetic diversity, which would negate the benefits of sexual reproduction. Thus, "normal" males (to focus on this portion of the species) are attracted to a variety of different female attributes; some men prefer thin females, other more sturdy shapes, some prefer large breasts, others not, different men are attracted preferentially to different body parts, etc. Nature endows the male inventory with a bell curve of sexual appetites, and as we move from the norm, we encounter all types of paraphilias that are not ultimately character defects, but the statistical and anomalous consequences of nature's quest for genetic diversity within the species. Nature has decided that it is OK to have a small percentage of the population have sexual orientations that incline away from reproduction as price to keep stirring the genetic pot. This may explain why there is no true homosexuality gene. If all sexual appetites were genetically determined, all types of genetic traits would cluster in discrete populations, and once again, the goal of genetic diversity would be frustrated.