Summary of Current Research
Michael A. Britt, Ph.D.
The Psych Files podcast
• Demographics: 3% of males and 2% of females 5%
of US population self identify as gay (260 million x .05
= 13 million)
• Sexual Behavior vs. Sexual Orientation
– An important distinction
– People can engage in homosexual behavior (ex:
experimentation in adolescence, homosexual behavior in
prison), but not have a homosexual orientation - Don Allen
• Sexual orientation is considered by many researchers
to be on a continuum
– On one end: those who are exclusively heterosexual and on
the other, those who consider themselves to be exclusively
homosexual with all degrees in between
Homosexuality among animals
• Necking and rubbing to sexual
excitement is common among male
• Common among pygmy chimpanzees
• Greylag geese can have homosexual
unions that last up to 15 years
between gays and straights
• Simon LeVay (1991)
– Neurobiologist at the Salk Institute in La Jolla
– The third interstitial nucleus (located in the
• is normally larger in men than in women
• in his sample of gay men, the third interstitial nucleus
was about the same size as in women
– Hypothalamus plays a role in sexual motivation
– Published in the Journal Science
– Critics: it can't be as black/white as this because
of the idea of a continuum
between gays and straights
– Lesbians are 91% more likely to be left
handed than heterosexual women
– Gay men are 34% more likely
• index (pointer) and ring finger
– Women: the length is more similar than in men
(men: bigger difference in the length of these two
– caused by exposure to male hormones in utero
– you can see this difference at age 2
– Lesbians: the difference is more similar to men
– suggests that lesbians may have had a greater
exposure to male hormones in the womb
• ”Fraternal Birth Order Effect" - James Cantor, et. al
• the more older brothers you have, the more likely a
male is to be gay
• doesn't matter what the sexual orientation of the older
• not true if your older brothers are step brothers or
• confirmed across cultures
• no relationship found for lesbians
• explanation: a change in the hormonal balance in the
mother's uterus with each additional child
– no difference in testosterone levels between adult
male hetero and homosexuals
• Spatial Abilities
– Mental Rotations task
– homosexual men perform more similarly to
– "...these spatial ability data suggest possible
biological and neuropsychological factors co-
related to the development of sexual orientation" -
– lesbians not sig different from heterosexual
• Adrenal Glands
• Age 10 (4th grade)
– The mean age of your first sexual attraction
• Between 6 and 8 the adrenal cortex begins to secrete
• Well before puberty
• same for hetero as for homo-sexual adults
– the time of your adrenal glands mature
• "...the biggest nongonadal source of sex steroids”
• "This biological process, distinctly different from
gonadarche, may underlie the development not only of
sexual attraction, but of cognition, emotions, motivations
and social behavior as well”
Genes: Twin Studies
– Dizygotic twins
• “fraternal twins” - two eggs, so they don't look alike
• 22% of twins of gay males were also gay
• 16% for lesbians
– Monozigotic twins
• "identical twins" (one egg)
• 52% of the identical twins of gay males were also gay”
• 48% for lesbians
– remember: this is not a perfect correlation, so
environment must play some part
Genes: Twin Studies
• focus: identical twins raised apart
– same genes, different environment
– so: if identical twins raised apart are both gay, that
argues for a genetic influence
– when one twin is gay, the chances that the other
one is gay are much higher than would be
– Results: Roger Hock: results are "quite consistent”
– higher, for example, than if the twins were
– but: even twins raised apart are not likely to be
raised in very different family environments
• Childhood Experiences
– Research by Bell, Weinberg & Hammersmith
– "..conducted face-to-face interviews with 979
homosexual participants (293 women and 686
men) and 477 heterosexual controls. The
researchers found no single condition of family life
or childhood experience that in and of itself
appeared to be a factor in either homosexual or
• Influence of Gay Parents
– Patterson, C.J. (2000). Family Relationships of
Lesbians and Gay Men, Journal of Marriage and
Family, 62, 1052-1069
– Mikach interviewed 75 gay fathers - only 7 of their
sons identified themselves as gay
– ... no significant problems in the development of
sexual identity among children of lesbian mothers
have yet been identified" - p. 1060
– "...gay men are no more likely than heterosexual
men to perpetrate child abuse (Jenny, Roesler, &
Poyer, 1994). Fears that children in custody of
gay or lesbian parents might be at heightened risk
for sexual abuse are without empirical foundation"
• Myths: Roger Hock: "resoundingly rejected" as
explanations for homosexuality:
– homosexual men have overly protective mothers and distant fathers
and homosexual women had overly protective fathers and distant
• If you know 1-3 gays who have a protective mother and distant
father - that's too small a sample size for confident conclusions
• Possible confirmation bias: how many heterosexual men do you
know who have a distant father and protective mother? We
often don't even think about looking at this
• The weakness of doing a survey on this issue: even if you find
support - which one is the causal factor? Did the parents cause
the child to be gay, or did the child's homosexuality cause the
parents to act this way?
– homosexuals were molested as children by a same sex adult (The
so-called "seduction hypothesis")
– homosexuals are more likely to have had a gay mother or father -
no evidence that homosexuality is more likely when children have
Nature AND Nurture
• EBE: "Exotic Becomes Erotic" theory
– Sandra Bem: Sexual orientation is a combination of in-born
temperament and experiences with other children
• male typical: aggressive, activity focused
• Female typical: relationship-oriented, non-aggressive
• temperament guides children toward "Gender conforming
• boys playing sports, "rough and tumble" play, girls play with
dolls, pretend activities
– Homosexuality results when:
• children with a temperament that doesn't match gender-typical
activities are drawn toward opposite sex activities and same
sex children are seen as "exotic”
• In adolescence, these feelings of the same sex being different,
naturally turn to feelings of attraction
– Critics: not much empirical support
• Wood, Wood & Boyd: The World of Psychology
– "Clearly there are no certain predictors of homosexuality”
• Brian Gladue
– "The presence of biological factors in the development of
homosexuality (and heterosexuality) is becoming
increasingly obvious. Already we have a set of reliable
findings, from many laboratories, demonstrating that human
sexual orientation has a genetic basis....”
– "...not all men and women arrive at their sexual orientation
following the same path.”
• The continuum: back to where we started
– The danger of black/white, gay/straight thinking. We're all
along that continuum somewhere.
– For some, their orientation was influenced by hormones in
the womb, others by events in their childhood.
– That's what's fascinating about the study of psychology.
• William Byne: The Biological Evidence
Challenged (1994, Scientific American)
– "While attempts to replicate these preliminary
finding continue, researchers and the public must
resist the temptation to consider them in any but
the most tentative fashion. Perhaps more
important, we should also be asking ourselves
why we as a society are so emotionally invested in
this research. Will it- or should it - make any
difference in the way we perceive ourselves and
others or how we live our lives and allow others to
live theirs? Perhaps the answers to the most
salient questions in this debate lie not within the
biology of human brains but rather in the cultures
those brains have created."
• Bailey, J.M., Bobrow, D., Wolfe, M., & Mikach, S. (1995). Sexual
Orientation of Adult Sons of Gay Fathers. Developmental Psychology,
31 (1), 124-129.
• Bell, A., Weinberg, M., & Hammersmith, S. (1981). Sexual preference:
Its development in men and women. Bloomington: Indiana University
• Bem, D.J. (1886). Exotic becomes erotic: A Developmental theory of
sexual attraction. Psychological Review, 103, 320-335.
• Byne, W. (1994). The Biological Evidence Challenged. Scientific
• Ciccarelli, S. & Meyer, G.F. (2006). Psychology. Prentice Hall.
• Cantor, J.M., Blanchard, R., Paterson, A.D. & Bogaert, A.F. (2002).
How many gay men owe their sexual orientation to fraternal birth order?
Archives of Sexual Behavior, 31, 1; Psychology Module.
• Carroll, M.P. (1998). But fingerprints don’t lie, eh?. Psychology of
Women Quarterly, 22, 739-749.
• Gladue, B.A, The BioPsychology of Sexual Orientation. in Current
Directions in Human Sexuality and Intimate Relationships, Fisher, T.D.
& McNulty, J. eds. Allyn and Bacon.
• Hock, R. (2010). Human Sexuality, 2e. Prentice Hall.
• Kendler, K.S., Thornton, L.M., Gilman, S.E., & Kessler, R.C. (2000).
Sexual orientation in a U.S. national sample of twin and nontwin sibling
pairs. The American Journal of Psychiatry, 157; 11; Health Module.
• King, B.M. (2005). Human Sexuality Today. Prentice Hall, 5e.
• Levay, S. (1991). A difference in hypothalamic structure between
heterosexual and homosexual men. Science, 253, 1034-1037.
• McClintock, M.K. & Herdt, G., Rethinking Puberty: The Development of
Sexual Attraction in Current Directions in Human Sexuality and Intimate
Relationships, Fisher, T.D. & McNulty, J. eds. Allyn and Bacon.
• Patterson, C.J. (2000). Family Relationships of Lesbians and Gay Men,
Journal of Marriage and Family, 62, 1052-1069
• Rind, B. (2001). Gay and bisexual adolescent boys' sexual experiences
with men: an empirical examination of psychological correlates in a
nonclinical sample. Archives of Sexual Behavior, 30 (4).
• Selekman, S. (2007). Homosexuality in children and their parents.
Pediatric Nursing, 33(5).
• Smith, B. (2007). The Psychology of Sex and Gender. Allyn and Bacon.
• Toates, F. (2007). Biological Psychology. Prentice Hall.
• Wood, S.E., Wood, E. G., & Boyd, D. (2005). The World of Psychology,
5e. Allyn and Bacon.
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