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Genes may time loss of virginity
14:36 31 March 2009 by Ewen Callaway
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Sexual precociousness is in our genes, new research
suggests. A unique study of twins separated at birth
finds a genetic link to the age at which a person
first engages in sexual intercourse.
"It's not like there's a gene for having a sex at a
certain date," says Nancy Segal, a psychologist at
California State University in Fullerton who led the
new study. Instead, heritable behavioural traits such
as impulsivity could help determine when people
first have sex, she says.
As genetic determinism goes, the new findings are
modest. Segal's team found that genes explain a
third of the differences in participants' age at first
intercourse – which was, on average, a little over 19
years old. By comparison, roughly 80% of variations
in height across a population can be explained by
genes alone.
However, determining the extent to which sexual
precociousness is inherited is trickier than making a
similar calculation for height. A common family
environment – whether it promotes or hinders early
sex – could cause scientists to overestimate the
effect of genes.
Social effect
By studying 48 pairs of twins raised apart, as well
as 23 individual twins, Segal's team sidesteps this
confounding factor. "This gives us a pure estimate
about how much genes affect behaviour," she says.
On the other hand, conservative social mores might
delay a teen's first sexual experience, causing
scientists to low-ball the effect of genes. Indeed,
Segal's team noticed a less pronounced genetic
effect among twins born before 1948, compared
with those who came of age in the 1960s or later.
Other factors may also make the effects of genes
harder to discern. For example, Segal's team also
found that female participants who felt unhappy
and unfulfilled in their home life were more likely to
have sex at a younger age.
Essential function
As for the specific genes involved, another team
previously found that a version of a gene encoding
a receptor for the neurotransmitter dopamine is
associated with age at first intercourse. Others have
linked the same version of the gene – called DRD4 –
to impulsive, risk-taking behaviour.
This might be one explanation for early sexual
activity, says Joseph Rodgers, a psychologist at the
University of Oklahoma in Norman. Yet unlike other
risky behaviours, such as drug use or reckless
driving, sex serves an essential biological function.
"For most of our evolutionary past, sexual
behaviour hasn't been risk taking, it's about
reproduction and success of the species," Rodgers
says.
Journal reference: Personality and Individual
Differences (DOI: 10.1016/j.paid.2009.02.010)
http://www.newscientist.com/article/...-time-loss-of-
virginity.html