Today's quote comes from a blog by Larry Arnhart called Darwinian Conservatism that I found through Secular Outpost. He makes a natural law case for homosexuality and gay marriage, and in it lists some facts regarding homosexuality found in nature. It is quite surprising how much we've documented. This is a great resource for anyone who denies there is evidence of this.
Scientists have observed homosexual behavior in 471 animal species--167 species of mammals, 132 species of birds, 32 species of reptiles and amphibians, 15 species of fishes, and 125 species of insects and other invertebrates (Bagemihl 1999, 673). Scientists have also observed that same-sex pairs have successfully reared young in at least 20 species. In some cases, one or both partners are the biological parent(s) of the young they raise together. In other cases, the partners adopt and care for young without being the biological parents (Bagemihl 1999, 23-26). Moreover, in some cases, the same-sex couples seem to be more successful in their parenting than opposite-sex parents.
We also now know that homosexuality is biologically natural in that it arises through the interaction of many biological factors in the early development of fetuses and children--genes and sex hormones shape the body and the brain in early life so that people are naturally predisposed to become heterosexual, bisexual, or homosexual. Monozygotic (identical) twins are more concordant in their sexual orientation than dizygotic (fraternal) twins, which clearly shows a genetic contribution to homosexuality That the concordance between monozygotic twins is about 50% suggests that while there is a genetic influence, there are also other biological factors involved. And while there is no single "gay gene," there are probably many different genes interacting with one another in various ways that influence sexual orientation (Poiani 2010, 55-96). Explaining the biology of animal homosexuality requires a complex multicausal model (Poiani 2010, 401-425).