The only thing unnatural is the classifcation of members of the human species into "gays" and "straights", i. e. the notion that man confines its sexual interaction a priori to exclusively one of 2 genders.Research indicates that various forms of this are found throughout the animal kingdom. As of 1999, nearly 1,500 species, ranging from primates to gut worms, have been observed engaging in same-sex behaviors; this is well documented in about 500 species.
Homosexual behavior in animals - Wikipedia, the free encyclopedia
There is zero evidence in the non-human animal animal kingdom of such confinement, among all the species identified above--not one of those species is, for example, gay--mates w/only members of the same sex.
It makes no sense at all that humans can claim that such a distinction exists when there's no evidence of it in other species.