Leiden Law Blog

What we can learn from fruit flies

What we can learn from fruit flies Balthasar van der Ast (1592-1657)

Usually the study of crime prevention is limited to psychological and sociological research on humans. Sometimes, however, interesting discoveries are made in the non-human world that could contribute to our understanding of crime prevention. Like a recent discovery in the world of the fruit fly!

The magic of female pheromones

Last November the Dutch newspaper Trouw reported that scientists at the University of California had discovered that a female fruit fly can reduce aggression in the male fruit fly considerably. When only male fruit flies gather together they can behave pretty aggressively towards one another. But when a single male fruit fly had been kept in close bodily contact with a single female for 24 hours, it turned out to be much less aggressive when it later joined the male group. The calming effect appears to have a molecular basis in the form of female pheromones, which are picked up by the hind legs of the male and then passed on as a signal to their brains. The effect lasts a couple of days.

A new manner for crime prevention?

The California scientists suspect a similar mechanism occurs in human beings, as the nerves, genes and brains of the fruit fly are closely related to ours. This link to the human world is very interesting. We know that (collective) male aggression is a big problem in our society, and is often the cause of criminal behaviour. If  close contact with a woman could reduce male aggression, even if only temporarily, this would have an important preventive effect on crime.
I remember Wim de Bie suggested a good few years ago – in the Dutch television program Keek op de Week, in which he, together with Kees van Kooten, humorously criticised Dutch society every Sunday night  – we could bring down hooliganism at soccer matches by allowing mothers to go along with their sons to the stadium. The recent research with fruit flies shows that perhaps we don’t have to go that far: if only men would spend a considerable amount of time before a match in close contact with a woman, this might be enough to  bring down the level of hooliganism.

Domestic Violence

But we needn’t cheer too soon. It’s easy to think of examples in our human world where there is no sign of any calming effect of the female pheromones. Think of the problem of domestic violence, for instance. Statistics show that a lot of human violence happens at home. In these cases it is usually the man who is violent, and the continuous female presence apparently has done very little to transform his aggression into calmer, more loving behaviour. Instead of this, the man even directs his aggression directly at the woman near him. Cases like these clearly show that the world of the fruit flies is also very different from the human world.

Learning from ‘lower creatures’

But we needn’t ignore the comparison completely either. After all, it’s interesting that since Darwin’s evolution theory we are gradually learning not only to recognize parts of ourselves in monkeys and apes, but also in the tiniest of insects. The behaviour of fruit flies can inspire us to look at human behaviour in a new way and also to ask some important new questions. Like: Did the Western world at certain periods become an aggressive, war-like world just because women were kept at a fair distance from men? And what sort of change can we expect now that women are increasingly spending long periods of time very close to men, whether at work or at home?

And perhaps along the way we may gain a little more respect for the tiny, defenceless fruit flies as they collectively and annoyingly gather around our fruit basket in the summer! 

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