Answer by Jim Ashby:
No, it's not. Homosexual behavior is abundantly documented in a number of species. Also, nature does not need all members of a species to procreate. Procreation is not the sole purpose of sex in some species (like bonobos). Also, we are intelligent, technological, human beings and, thus, somewhat removed from nature. The birth control pill, for instance, can minimize concern for pregnancy and, thus, minimize the role of procreation in sex.