Homosexuality requires no defense. It exists and the preference for a same-gender partner is a clear function of a right hemisphere process. The suggestion therefore of homosexuality in animals as a defense for same gender sexuality in not necessary.
A valid question for investigation as to whether there is same-gender preference in animals is worthy however of consideration.
First we must remember that the sexual act has as its natural motive reproduction. Second we must recognize that that act is an act which we may psychologically discern as the domination of the male gender.
We do see in almost all animals a posture of copulation, indeed we have often experienced a male or even a female dog mounting one's leg.
This does not always mean that the dog is exhibiting sexual frustration or mistaking your leg for a female. It can mean that the animal is in the face of a new stimulus attempting to establish dominance in one way or another.
"Dogs will also mount one another because of the strength of their reaction to the smell of an estrus female: The smell of a female dog in heat can instigate a frenzy of mounting behaviors. Even other females who are not in heat will mount those who are. Males will mount males who have just been with estrus females if they still bear their scent... And males who catch wind of the estrus odor may mount the first thing that they come into contact with."
So mounting behavior in and of itself does not mean that there is a selective process at work.
Dr. Charles Socarides of the National Association for Research and Therapy of Homosexuality (NARTH) observes: The term homosexuality should be limited to the human species, for in animals the investigator can ascertain only motor behavior. As soon as he interprets the animal's motivation he is applying human psychodynamics--a risky, if not foolhardy scientific approach.
However we cannot take the opposite point of view and say that homosexual behavior in the human creature is also an outcome of mistaken physiological choice or dominance.
That homosexuality is not a modern phenomenon is certain as we see that "many Native American tribes formally recognize--and honor--human homosexuality and transgender in the role of the 'two-spirit' person (sometimes formerly known as berdache). The 'two-spirit' is a sacred man or woman who mixes gender categories by wearing clothes of opposite or both sexes .... And often engaging in same -sex relations."
So here we must forget animal homosexuality and generate our investigations towards the natural homosexual preference in human creatures.
What is important is this idea of the "two-spirit" personality in the human creature who has the sensory capacity not only to select a same-gender sexual partner, but to assume quite naturally the behavioral consequences of "two-spirit personality".