Weinberg, Williams and Pryor explore the riddle of dual attraction in their study of 800 residents in San Francisco. Fieldwork, intensive interviews and surveys provided data about the nature of bisexual attraction, the steps that lead people to become bisexual and how sexual preference can change over time. They found that heterosexuals, more than homosexuals, become bisexual; that bisexual men and women differ markedly in their sexual behaviour and romantic feelings; that most bisexuals ultimately settle into long-term relationships while continuing sexual activity outside those relationships; and they also explain why transexuals often become bisexual. Moreover, the authors discovered that as the AIDS crisis unfolded, many bisexual men entered into monogamous relationships with women, and bisexual women into more lesbian relationships.