Homosexuality per se is an example of normal and positive variation in human sexual orientation

American Psychological Association (APA)

The longstanding consensus of the behavioral and social sciences and the health and mental health professions is that homosexuality per se is a normal and positive variation of human sexual orientation (Bell, Weinberg & Hammersmith, 1981; Bullough, 1976; Ford & Beach 1951 ; Kinsey, Pomeroy, & Martin, 1948; Kinsey, Pomeroy, Martin, & Gebhard, 1953 ). Homosexuality per se is not a mental disorder (APA, 1975). Since 1974, the American Psychological Association (APA) has opposed stigma, prejudice, discrimination, and violence on the basis of sexual orientation and has taken a leadership role in supporting the equal rights of lesbian, gay, and bisexual individuals (APA, 2005).

Homosexual behavior in animals (via Wikipedia)

Homosexual and bisexual behavior are widespread in the animal kingdom: a 1999 review by researcher Bruce Bagemihl shows that homosexual behavior has been observed in close to 1500 species, ranging from primates to gut worms, and is well documented for 500 of them. Animal sexual behavior takes many different forms, even within the same species. The motivations for and implications of these behaviors have yet to be fully understood, since most species have yet to be fully studied. According to Bagemihl, "the animal kingdom [does] it with much greater sexual diversity -- including homosexual, bisexual and nonreproductive sex -- than the scientific community and society at large have previously been willing to accept."