Daryl Bem, PhD, Professor of Psychology at Cornell University, wrote in a 2000 article titled "Exotic Becomes Erotic: Interpreting the Biological Correlates of Sexual Orientation" in Archives of Sexual Behavior:
"The central proposition of EBE [Exotic Becomes Erotic] theory is that individuals can become erotically attracted to a class of individuals from whom they felt different during childhood...
[B]iological variables such as genes or prenatal hormones do not code for sexual orientation per se but for childhood temperaments, such as aggression and activity level. A child's temperaments predispose him or her to enjoy some activities more than other activities. One child will enjoy rough-and-tumble play and competitive team sports (male-typical activities); another will prefer to socialize quietly or play jacks or hopscotch (female-type activities)...
The most common reasons given by gay men and lesbians for having felt different from same-sex peers in childhood were sex-atypical preferences and behaviors in childhood--gender nonconformity. In fact, childhood gender conformity or nonconformity was not only the strongest but the only significant childhood predictor of later sexual orientation for both men and women."
J. Michael Bailey, PhD, Professor of Psychology at Northwestern University, and Kenneth Zucker, PhD, Psychologist-in-Chief at the Centre for Addiction and Mental Health at the University of Toronto, wrote in their 1995 article titled "Childhood Sex-Typed Behavior and Sexual Orientation: A Conceptual Analysis," in Developmental Psychology:
"As our analyses demonstrated for both men and women, research has firmly established that homosexual subjects recall substantially more cross-sex-typed behavior in childhood than do heterosexual subjects...
[E]arly cross-gender behavior appears to be substantially more predictive of homosexuality in men than in women. Because a strong empirical link between childhood sex-typed behavior and sexual orientation has been established for men in both prospective and retrospective, it is likely to be genuine."
Dean Hamer, PhD, former Chief of the Section on Gene Structure and Regulation in the Laboratory of Biochemistry at the National Cancer Institute, and Peter Copeland, wrote in their 1994 book The Science of Desire: The Search for the Gay Gene and the Biology of Behavior:
"Most sissies will grow up to be homosexuals, and most gay men were sissies as children.
Despite the provocative and politically incorrect nature of that statement, it fits the evidence. In fact, it may be the most consistent, well-documented, and significant finding in the entire field of sexual-orientation research and perhaps in all of human psychology."
Richard Friedman, MD, Clinical Professor of Psychiatry at Weill Medical College of Cornell University, stated in his 1988 book Male Homosexuality: A Contemporary Psychoanalytic Perspective:
"A history of gender identity pathology (including effeminacy and chronic extreme unmasculinity) is much more common among men who are predominantly or exclusively homosexual than among men who are predominantly or exclusively heterosexual.
The childhood finding seems to be associated with homosexuality per se, distributed both across all types of psychopathology and among men without significant psychopathology. At present, I believe this is the only correlation between psychopathology and homosexuality that may be taken as an established fact...
The combined results of numerous investigations lead to the conclusion that childhood gender identity/gender role disturbances are associated with predominant or exclusive homosexuality in adulthood. Absence of such disturbance diminishes the likelihood that a boy will become a man who is exclusively or predominantly homosexual."
Archives of Sexual Behavior published a 1995 article by G. Phillips and Ray Over titled "Differences between Heterosexual, Bisexual, and Lesbian Women in Recalled Childhood Experiences," that stated:
"Not all boys who engage in high levels of gender nonconforming behaviors or low levels of gender conforming behaviors demonstrate homosexual orientation as an adult; nor do all adult homosexual men report having experienced high levels of gender nonconforming behaviors or low levels of gender conforming behaviors in childhood."
Journal of Gender Studies published a 2003 article titled "Same-Sex Sexuality and Childhood Gender Non-conformity: A Spurious Connection," by Lorene Gottschalk, that stated:
"Gender non-conformity is believed by many researchers and theorists of same-sex sexuality to be the behavioural expression of congenital gender inversion. Hence from such a perspective, a 'homosexual', that is, a gender invert, will behave in gender non-conforming ways from early childhood. Childhood gender non-conformity inevitably includes stereotypical activities such as avoidance of rough and tumble play for boys and engaging same for girls, commonly known as tomboy and sissy behaviour...
Feminist approaches reject the idea that same-sex sexuality is about gender inversion. This perspective recognises that the sexual self is moulded by social forces and conscious will, that all human beings are born with the potential to be sexual, rather than with a particular sexual orientation, and that the direction of sexual preference, or sexual orientation, is socially determined, and influenced by the values and social arrangements of the dominant culture...
The connection between gender non-conformity and adult sexuality, too, is socially constructed."
Vern Bullough, PhD, Professor Emeritus at California State University North Rigdg and Bonnie Bullough, PhD, Former Dean of the State University of New York at Buffalo Nursing School, wrote in their 1993 article "The Causes of Homosexuality: A Scientific Update," published in the magazine Free Inquiry:
"Not all cross-gendered children became homosexual. Rather, the data suggest that a childhood cross-gender identity and behavior is the precursor to four types of adult patterns: homosexuality; adult cross-dressing (transvestism); trans-sexualism; and ordinary heterosexuality without any discernible non-normative sex pattern. The strength of the urge for the cross-gendered behavior and the social learning that takes place probably helps to determine the pattern of adult behavior."
GLBTQ, an online encyclopedia of gay, lesbian, bisexual, transgender, and queer culture stated in its 2004 entry for "Tomboy":
"The word 'tomboy' has come to mean a frolicsome girl given to sport and other boyish ways.
Throughout their history, tomboys have had to contend with the stigma of presumed lesbianism or the accusation of wanting to be male. Both assumptions were categorically refuted by twentieth-century psychology, which established the normalcy of the tomboy experience among girls of all [sexual] identities."