Addressing the ways in which etiology, the science of causes, has come to dominate discussions of gay and lesbian politics, this essay examines traces of evolutionary theory in recent right-wing rhetoric against gay marriage from such organizations as the Family Research Council, as well as in ostensibly pro-gay claims that homosexuality is not acquired but biologically determined. Invoking Darwin, antigay groups claim that same-sex marriage will lead to human extinction because it does not serve the propagation of the species. However, this insistence on homosexual sterility is in fact driven by a fear of queer increase. This essay proposes that antigay rhetoric tacitly construes same-sex desire as a meme, a unit of cultural meaning believed to recur and mutate like a gene. In this phobic view of gay etiology, then, homosexuality is a dangerous idea that proliferates more successfully than heterosexual reproduction. In response, queer communities increasingly claim that homosexuality is immutable and essential, citing scientists’ theories of biological determinism to support the more colloquial notion that they are born gay. Many such theories, however, share the evolutionary and reproductive language used by the religious Right, seeking to prove homosexuality both memetically and genetically sterile. Reading popular publications on biological causes of homosexuality, this article shows how “born gay” and “gay gene” discourses produce their own vulgar Darwinism, echoing the voices they would oppose.