WASHINGTON In a study that sheds light on the
biology of aggression, scientists swapped genes in
gender-bending fruit flies to make boys fight like girls and
girls fight like boys.
Researchers from Harvard Medical School and the Institute
of Molecular Pathology in Vienna focused on a gene in fruit
flies dubbed "fruitless," an important player in behavioral
differences between the sexes of these insects.
The gene is known for its role in male courtship, but also
controls another sex-specific behavior -- how flies fight,
according to the research appearing on Sunday in the journal
When they fight, female fruit flies rely on maneuvers like
shoving and head butts to an opponent's body. Males use tactics
that include lunging, boxing and rearing up on their back legs
and snapping down their forelegs to flatten an adversary.
The researchers swapped the male and female versions of the
gene in fruit flies and observed the consequences. Males with
the feminine gene used female fighting tactics, while the
females with the masculine gene fought like the boys.
People have a lot to learn about the biological basis of
aggression, said Harvard neurobiologist Edward Kravitz, one of
the study's authors.
"It goes without saying aggression, as well as violence, in
society is a serious problem. It has to have biological roots.
And the biological roots will have genetic components and
experiential components," Kravitz said in an interview.
It is important to learn about such complex behaviors in a
simple organism, and then apply this knowledge to higher and
higher forms while ultimately trying to gain insight into human
behavior, Kravitz said.
People do not have an exact equivalent to the "fruitless"
gene, Kravitz added, but probably have other human genes
serving similar functions.
Kravitz said his team, pondering how to instigate fruit fly
fights, settled on food and mating -- or, in this case,
They set up the insect world's equivalent to a steel-cage
match -- a chamber with glass walls and a lid with air holes, a
dish of fly food and a mate -- and sent in the combatants. But
when they used a live female fly as a lure for the males, she
often would just fly off.
"My student discovered when he transferred the female to
the dish and accidentally crushed her head that the males
didn't care whether she had a head or not. That's a true story
of what led us to cutting the heads of the females off in
subsequent studies," Kravitz said.
"They'll court the dead, headless female fly, and try to
copulate with her sometimes."
In a related study in the Proceedings of the National
Academy of Sciences last week, Kravitz and colleagues wrote
that flies developed "winner" or "loser" mentalities in these
fights, which amounted to a series of nonlethal skirmishes.
Kravitz acknowledged some of the nutty aspects of the
"When you're trying to explain this to your children --
'Dad, what did you do today?' 'Well, I had these two fruit
flies, son, and I was trying to figure out how to get them to
fight.' Just think of that."