http://www.scientificblogging.com/news_releases/homo***uality_a_result_of_ge=
netics_and_random_environmental_factors_says_twins_study
Homo***uality A Result Of Genetics And Random Environmental Factors,
Says Twins Study
Submitted by News Account on 28 June 2008 - 5:27pm. Applied Science
Homo***ual behavior is largely shaped by genetics and random
environmental factors, according to findings from the world's largest
study of twins.
Researchers from Queen Mary's School of Biological and Chemical
Sciences and Karolinska Institutet in Stockholm re****t in the Archives
of ***ual Behavior that genetics and environmental factors (which are
specific to an individual, and may include biological processes such
as different hormone exposure in the womb), are im****tant determinants
of homo***ual behavior.
The team led by Dr Niklas L=E5ngstr=F6m at Karolinska Institutet conducted
the first truly population-based survey of all adult (20-47 years old)
twins in Sweden. Studies of identical twins and non-identical, or
fraternal, twins are often used to untangle the genetic and
environmental factors responsible for a trait. While identical twins
share all of their genes and their entire environment, fraternal twins
share only half of their genes and their entire environment.
Therefore, greater similarity in a trait between identical twins
compared to fraternal twins shows that genetic factors are partly
responsible for the trait.
Dr Qazi Rahman, study co-author and a leading scientist on human
***ual orientation, explains: "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'
homo***uality - the factors which influence ***ual orientation are
complex. And we are not simply talking about homo***uality here -
hetero***ual behaviour is also influenced by a mixture of genetic and
environmental factors.
The study looked at 3,826 same-gender twin pairs (7,652 individuals),
who were asked about the total numbers of opposite *** and same ***
partners they had ever had. The findings showed that 35 per cent of
the differences between men in same-*** behavior (that is, that some
men have no same *** partners, and some have one or more) is accounted
for by genetics. Rahman explains:
"Overall, genetics accounted for around 35 per cent of the differences
between men in homo***ual behaviour and other individual-specific
environmental factors (that is, not societal attitudes, family or
parenting which are shared by twins) accounted for around 64 per cent.
In other words, men become gay or straight because of different
developmental pathways, not just one pathway."
For women, genetics explained roughly 18 per cent of the variation in
same-*** behavior, non-shared environment roughly 64 per cent and
shared factors, or the family environment, explained 16 per cent.
The study shows that genetic influences are im****tant but modest, and
that non-shared environmental factors, which may include factors
operating during foetal development, dominate. Im****tantly, heredity
had roughly the same influence as shared environmental factors in
women, whereas the latter had no impact on ***ual behavior in men.
Dr Rahman adds: "The study is not without its limitations - we used a
behavioural measure of ***ual orientation which might be ok to use for
men (men's psychological orientation, ***ual behaviour, and ***ual
responses are highly related) but less so for women (who show a
clearer separation between these elements of ***uality). Despite this,
our study provides the most unbiased estimates presented so far of
genetic and non-genetic contributions to ***ual orientation."
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