SummaryOngoing political controversies around the world exemplify a long-standing and widespread preoccupation with the acceptability of homosexuality. Nonheterosexual people have seen dramatic surges both in their rights and in positive public opinion in many Western countries. In contrast, in much of Africa, the Middle East, the Caribbean, Oceania, and parts of Asia, homosexual behavior remains illegal and severely punishable, with some countries retaining the death penalty for it. Political controversies about sexual orientation have often overlapped with scientific controversies. That is, participants on both sides of the sociopolitical debates have tended to believe that scientific findings-and scientific truths-about sexual orientation matter a great deal in making political decisions. The most contentious scientific issues have concerned the causes of sexual orientation-that is, why are some people heterosexual, others bisexual, and others homosexual? The actual relevance of these issues to social, political, and ethical decisions is often poorly justified, however.

Although it is typically presumed that heterosexual individuals only fall in love with other-gender partners and gay-lesbian individuals only fall in love with same-gender partners, this is not always so. The author develops a biobehavioral model of love and desire to explain why. The model specifies that (a) the evolved processes underlying sexual desire and affectional bonding are functionally independent; (b) the processes underlying affectional bonding are not intrinsically oriented toward other-gender or same-gender partners: (c) the biobehavioral links between love and desire are bidirectional, particularly among women. These claims are supported by social-psychological, historical, and cross-cultural research on human love and sexuality as well as by evidence regarding the evolved biobehavioral mechanisms underlying mammalian mating and social bonding.

Debates persist over whether bisexuality is a temporary stage of denial or transition, a stable "3rd type" of sexual orientation, or a heightened capacity for sexual fluidity. The present study uses 5 waves of longitudinal data collected from 79 lesbian, bisexual, and "unlabeled" women to evaluate these models. Both the "3rd orientation" and "fluidity" models had support, but the "transitional stage" model did not. Over 10 years, 2/3 of women changed the identity labels they had claimed at the beginning of the study, and 1/3 changed labels 2 or more times. Yet, contrary to the "transitional stage" model, more women adopted bisexual/unlabeled identities than relinquished these identities; few bisexual/unlabeled women ended up identifying as lesbian or heterosexual. Overall, the most commonly adopted identity was "unlabeled." Bisexual/unlabeled women had stable overall distributions of same-sex/other-sex attractions but greater absolute fluctuations in attractions from assessment to assessment than lesbians. All women reported declines in their ratio of same-sex to other-sex behavior over time. These findings demonstrate that the distinction between lesbianism and bisexuality is a matter of degree rather than kind.

Previous research suggests that the sexual identities, attractions, and behaviors of sexual-minority (i.e., nonheterosexual) women change over time, yet there have been few longitudinal studies addressing this question, and no longitudinal studies of sexual-minority youths. The results of 2-year follow-up interviews with 80 lesbian, bisexual, and "unlabeled" women who were first interviewed at 16-23 years of age are reported. Half of the participants changed sexual-minority identities more than once, and one third changed identities since the first interview. Changes in sexual attractions were generally small but were larger among bisexuals and unlabeled women. Most women pursued sexual behavior consistent with their attractions, but one fourth of lesbians had sexual contact with men between the two interviews. These findings suggest that there is more fluidity in women's sexual identities and behaviors than in their attractions. This fluidity may stem from the prevalence of nonexclusive attractions among sexual-minority women.

There have been many anecdotal accounts of individuals who self-identify as lesbian, gay, or bisexual only to relinquish these identities later. The current study examines this phenomenon among a sample of young nonheterosexual women who underwent 3 interviews over a 5-year period. Over a quarter of these women relinquished their lesbian/bisexual identities during this period: half reclaimed heterosexual identities and half gave up all identity labels. These women did not differ from those who maintained lesbian/bisexual identities regarding the age at which they underwent sexual identity milestones, the factors that precipitated their sexual questioning, or their recollection of childhood "indicators" of same-sex sexuality. Women who relinquished their identities for heterosexual identities had smaller ratios of same-sex to other-sex attractions across the 5-year assessment period, but their attractions did not significantly change. Only 1 woman described her previous same-sex identification as a phase; the rest emphasized changes in how they interpreted or acted on their attractions. I acknowledge the participation and assistance of the recruitment sites, as well as Ritch Savin-Williams for comments on an earlier version of this article.