MONDAY, June 30 (HealthDay News) -- Genetics and random
environmental factors each play a major role in determining both
gay and heterosexual behavior, say British and Swedish
researchers.
"This study puts cold water on any concerns that we are looking
for a single 'gay gene' or a single environmental variable which
could be used to 'select out' homosexuality -- the factors which
influence sexual orientation are complex. And we are not simply
talking about homosexuality here -- heterosexual behavior is also
influenced by a mixture of genetic and environmental factors,"
study co-author Dr. Qazi Rahman, a leading scientist on human
sexual orientation, said in a prepared statement.
Environmental factors are specific to an individual and may
include biological processes such as different hormone exposure in
the womb, the researchers noted.
The researchers studied more than 3,800 same-gender twin pairs,
ages 20 to 47, in Sweden. The twins were asked about the total
numbers of opposite sex and same sex partners they had ever
had.
"Overall, genetics accounted for around 35 percent of the
differences between men in homosexual behavior and other
individual-specific environmental factors (that is, not societal
attitudes, family or parenting which are shared be twins) accounted
for around 64 percent. In other words, men become gay or straight
because of different developmental pathways, not just one pathway,"
Rahman said.
Among the female twins, genetics explained about 18 percent of
the variation in sexual orientation, non-shared environmental
factors 64 percent, and family environment 16 percent.
It's important to note that heredity and shared environment had
roughly the same influence in women, while shared environment had
virtually no impact on men's sexual behavior, the researchers
said.
The study, which was published in the journal
Archives of Sexual Behavior, shows that while genetic
factors are important, non-shared environmental factors are
dominant in determining sexual orientation.
"This study is not without its limitations -- we used a
behavioral measure of sexual orientation which might be okay to use
for men (men's psychological orientation, sexual behavior, and
sexual responses are highly related) but less so for women (who
show a clearer separation between these elements of sexuality),"
Rahman noted. "Despite this, our study provides the most unbiased
estimates presented so far of genetic and non-genetic contributions
to sexual orientation."
More information
The American Psychological Association has more about
sexual orientation.
