One universal principle – opposites attract – accounts for homosexuality as well as heterosexuality, according to a Cornell University psychologist who proposes a sweeping new theory of how sexual orientation develops.

Lifelong sexual orientations can be traced to childhood preferences for sex-typical or sex-atypical activities and peers, suggests Daryl J. Bem, Cornell professor of psychology. “Gender-conforming” children, who prefer sex-typical activities and peers, come to feel different from opposite-sex peers, perceiving them as dissimilar, unfamiliar and exotic. And “gender-nonconforming” children, who prefer sex-atypical activities and peers, come to feel different from same-sex peers. As children reach puberty, the feelings of being different get transformed into sexual or romantic attraction: The exotic becomes erotic, or EBE.

Bem first outlined the EBE theory – complete with a six-step sequence that starts with “biological variables” such as genes and prenatal hormones – in the peer-reviewed journal, Psychological Review (1996, Vol. 103, No. 2), and now is working on a book-length exposition.

The social psychologist believes that biological variables may play an indirect role but do not directly determine sexual orientation. Rather, biology can be partially responsible for what he calls childhood temperaments, and youngsters’ temperaments predispose them to enjoy some activities more than others during the critical, life course-setting period.

Many pre-adolescent boys and some girls, Bem observes, enjoy what our society considers “male-typical” activities – rough-and-tumble play and competitive sports – and they tend to associate with peers who share their preferences. Likewise, many girls and some boys are predisposed by temperament toward “female-typical” activities, such as socializing quietly or playing hopscotch, and they seek like-minded peers.

The gender-nonconforming kids who prefer sex-atypical activities and opposite-sex playmates don’t have an easy time of it, as every parent knows:;Nonconforming boys who play with girls are taunted as “sissies” by typical boys, who consider girls “yucky.” And typical girls, who feel intimidated by boys, may shun the “tomboys” for their nonconformity.

Eventually, children develop an attraction for those they find exotic: Sex-typical children will become attracted to the opposite sex; sex-atypical children will become attracted to the same sex. This occurs, Bem maintains, because every child – whether conforming or nonconforming – experiences “heightened physiological arousal in the presence of peers from whom he or she feels different. In later years this arousal is transformed to erotic and/or romantic attraction.”

Obviously, not every “sissy” boy becomes a gay man. Nor does every “tomboy” grow to be a lesbian woman, Bem acknowledges.&; But many do. The Cornell psychologist points to a series of studies, including a meta-analysis of 48 studies totaling thousands of participantsanalysis (by J.M. Bailey and K.J. Zucker) shows that gay men and lesbians are significantly more likely to recall gender-nonconforming behaviors and interests in childhood than are heterosexual men and women. In one study that followed males from childhood through late adolescence to adulthood, about 75 percent of the previously gender-nonconforming boys became homosexual or bisexual.

“The key is: Did you feel more like your own sex or the opposite sex during that formative period,” Bem said. “You are likely to feel an attraction for those who were different, exotic, opposite – whether or not they were of the opposite sex.” The EBE theory treats homosexuality and heterosexuality as the same phenomenon, Bem noted.

Asked if he believes there is a “gay gene,” Bem answers, “I doubt that very much. My theory challenges the biological theory that sexual orientation is embedded in the genes – not by refuting biology but by reinterpreting it. I believe that sexual orientation per se is not coded in genetics, in brain neuroanatomy or in prenatal hormones. Rather, biology influences childhood temperaments and preferences that lead us to feel different from either opposite-sex or same-sex peers and to perceive them as exotic. Then the exotic becomes erotic.”

Aware that his theory is likely to raise controversial issues, Bem has written an unpublished “Political Postscript” to address some questions. Among them: Could the theory be misused to implement an anti-gay strategy for preventing gender-nonconforming children from becoming homosexual adults? It will not, he believes.

Moreover, Bem challenges the view that people will be more tolerant of homosexuality if they believe that it is determined by biology. Indeed, the gay community should be happy with EBE theory, he said, “because it views heterosexuality as no more biologically natural than homosexuality.”