7 September 2019 | New Scientist | 9THE largest ever genetic study of
sexual behaviour has found that
many genes influence sexuality,
each with tiny effects.
Previous studies have
identified individual genes that
may influence sexual orientation
in boys and men. But these
studies have all been too small
to pin down any genetic drivers
of sexuality.
Robbee Wedow at the Broad
Institute of MIT and Harvard
and his colleagues collected
data from the UK Biobank
and the genetic testing firm
23andMe. Both organisations
ask the genomes’ owners
about their sexual behaviour.
This gave the team genetic
data and information on the
sexual behaviour of around
477,000 people.
First, the team compared the
genomes of people who said
they’d had sex with people of
the same sex with those who
reported only heterosexual
behaviour. They found that a
person’s genes could together
explain around a third of
whether they’d had same-sex
experiences or not.
Next, the team was able toidentify five specific genetic
variants that were associated
with same-sex experiences to
a statistically significant degree.
Two of these were in both men
and women, two were specific
to men and one was specific
to women.
All five genes had only a small
effect and were far from being
predictive of whether a person
had had sex with a person of the
same sex. Since the team had
already found that a third of the
variation in sexual behaviourcan be explained by a person’s
genes, this suggests that there
are many other genes that
contribute at a very low level.
The team says there could be
thousands of them. “Our results
really underscore that this
behaviour is a normal part of
human variation,” says Wedow.
“Because we have so many
different [genetic regions]
involved, it implies that there
are multiple genetic ways to
end up queer,” says Jeremy
Yoder at California State
University Northridge. “And
that’s kind of a poetic idea.” ❚contain a gene that allows the
plant to make an insecticide.
But these are banned in many
African countries and may be
too expensive for smallholders
to use anyway. “The economic
model is going to be very different
and I don’t know how you make it
compatible with the smallholder
situation,” says Melanie Bateman
at CABI’s office in Delémont,
Switzerland.
Another possible solution
would be to use a pesticide.
A study from researchers in
Ethiopia this year looked at a range
of commercial pesticides and
found four of them effectively
killed 90 per cent of the pests after
72 hours. But the UN’s Food and
Agriculture Organization says
pesticides should only be part of
a package of measures. If used
inappropriately, they can have
negative side effects, such as
killing parasitoid wasps. Bateman
says there are better alternatives
such as the pesticidal oil of the
south Asian neem tree and
viruses or nematode worms that
specifically attack armyworms.
Meanwhile, the caterpillars are
still marching. In 2018, they were
spotted in India, then Sri Lanka,
Yemen and Myanmar. This year,
they have been confirmed in
China and, as of July, they are in
Japan too. Day and his colleagues
say Australia could be next.
There is one saving grace:
the pest can’t survive freezing
temperatures, which should
limit its spread north. But there
are a few places in Europe where
it could overwinter and many
others where it could live during
warmer months. The one thing
stopping it reaching Europe at
the moment is the natural barrier
of the Sahara desert. “But with
time it’ll spread across northern
Africa,” says Day. “Then it’s an easy
hop into Europe.” ❚insect by rearing armyworms
and watching to see what
emerges from within them.
However, the most promising
wasp appears to be Telenomus
remus. This species is known to
target armyworms in South
America and was being considered
for import when, in March,
researchers reported that it was
already established in at least five
African countries. This means it
could be reared and released in
large numbers without such
stringent safety testing.
There are other strategies.
One would be to use GM crops that“Unchecked armyworm
infestations could destroy
more than half of the
maize grown in Africa”
Fall armyworms, like
this one in Thailand,
love to feast on maizeREUTERS/SOE ZEYA TUN4 77,
Number of people in the largest
genetic study of sexual behaviourGenomicsJessica HamzelouThousands of genes
may be involved in
driving our sexualityZOLTAN GALANTAI/ALAMY STOCK PHOTOThere is no such
thing as a ‘gay gene’