Book excerpt: What makes people gay, lesbian, bisexual, or heterosexual? And who cares? Written by one of the leading scientists in the research of sexual orientation, Queer Science looks at how scientific discoveries about homosexuality influence society's attitude toward gays and lesbians, beginning with the theories of the German sexologist and gay-rights pioneer Magnus Hirschfeld and culminating with the latest discoveries in brain science, genetics, endocrinology, and cognitive psychology.