Humans can fall anywhere along a continuous scale of sexual orientation, although most humans are heterosexual. While homosexual behavior occurs in many other animals, only humans and domestic sheep have so far been found to exhibit exclusive preference for same-sex relationships. Most evidence supports nonsocial, biological causes of sexual orientation, as cultures that are very tolerant of homosexuality do not have significantly higher rates of it. Research in neuroscience and genetics suggests that other aspects of human sexuality are biologically influenced as well.