Professor of Psychology at Northwestern University
Not Clearly Pro or Con to the question "Is Sexual Orientation Determined at Birth?"
"It is important not to equate 'inborn' with 'genetic.' Environment can matter yet affect sexual orientation before birth. One of the most interesting hypotheses right now concerns fraternal birth order, or the number of older brothers a man has. The more older brothers a man has, the more likely the man’s orientation will be homosexual. Furthermore, it appears it's the number of older brothers that were inside his mother’s uterus, and not the number of older brothers that were in his house–that is, it's an innate and not a social influence. Gay men with identical twins usually have straight identical twins. So environment matters. I think, however, it's not the social environment, but more likely the early womb environment.
Also, I would separate men and women. I am much less confident that women's sexual orientation is inborn."
[Editor's Note: In an Aug. 21, 2017 email in reply to our question whether a categorization of 'not clearly pro or con' would accurately fit his position, Bailey stated, "Sure, or you could say Males: 'Yes' Females: 'Uncertain.'"]
Cowritten with Adam Safron, David Sylva, Victoria Klimaj, A.M. Rosenthal, et al., "Neural Correlates of Sexual Orientation in Heterosexual, Bisexual, and Homosexual Men," Scientific Reports, Feb. 1, 2017
Cowritten with Paul L. Vasey, Lisa M. Diamond, S. Marc Breedlove, Eric Vilain, and Marc Epprecht, "Sexual Orientation, Controversy, and Science," Psychological Science in the Public Interest, 2016
Cowritten with A.M. Rosenthal, D. Sylva, and A. Safron, "Sexual Arousal Patterns of Bisexual Men Revisited," Biological Psychology, July 2011
Cowritten with Adam Greenberg, "Liberty Should Win: We May Choose Our Children's Sexual Orientation," thehastingscenter.org, June 27, 2007
Cowritten with G. Rieger and M. Chivers, "Sexual Arousal Patterns of Bisexual Men," Psychological Science, 2005
The Man Who Would Be Queen: The Science of Gender-Bending and Transsexualism, 2003
Cowritten with Aaron S. Greenberg, "Parental Selection of Children's Sexual Orientation," Archives of Sexual Behavior, 2001
Cowritten with Michael P. Dunne and Nicholas G. Martin, "Genetic and Environmental Influences on Sexual Orientation and Its Correlates in an Australian Twin Sample," Journal of Personality and Social Psychology, Mar. 2000
Cowritten with Khytam Dawood, Richard C. Pillard, Christopher Hovarth, and William Revelle, "Familial Aspects of Male Homosexuality," Archives of Sexual Behavior, 2000
Cowritten with R.C. Pillard, K. Dawood, M.B. Miller, L.A. Farrer, et al. "A Family History Study of Male Sexual Orientation," Behavioral Genetics, 1999
Cowritten with Peggy Y. Kim, Alex Hills, and Joan A. W. Linsenmeier, "Butch, Femme, or Straight-Acting? Partner Preferences of Gay Man and Lesbians," Journal of Personality and Social Psychology, Nov. 1997
Cowritten with Kenneth K. Zucker, "Childhood Sex-Typed Behavior and Sexual Orientation: A Conceptual Analysis and Quantitative Review," Developmental Psychology, Jan. 1995
Cowritten with R.C. Pillard, "Genetics of Human Sexual Orientation," Annual Review of Sex Research, 1995
Cowritten with A.P. Bell, "Familiarity of Female and Male Homosexuality," Behavioral Genetics, 1993
Cowritten with R.C. Pillard, "A Genetic Study of Male Sexual Orientation," Archives of General Psychiatry, 1991