Re the monkey comments, homosexual, as well as bisexual behavior is widespread in the animal kingdom. A 1999 review by researcher Bruce Bagemihl shows that homosexual behavior, not necessarily sex, has been observed in close to 1500 species, ranging from primates to gut worms, and is well documented for 500 of them.

The bonobo (an ape), which has a matriarchal society (unusual amongst apes), is a fully bisexual species -- both males and females engage in heterosexual and homosexual behavior, being noted for lesbianism in particular. About 60% of all sexual activity in this species is between two or more females. While the homosexual bonding system in bonobos represent the highest frequency of homosexuality known in any species, homosexuality has been reported for all great apes, including humans, as well as a number of other primate species. (wikipedia, citing multiple sources)