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© Sipa Press/Rex FeaturesGerman neo-Nazis feeling the love of the pack at a demonstration.
Carsten de Dreu, 44, a professor of psychology at the University of Amsterdam, describes himself as a social psychologist with an interest in evolutionary theory. He is president of the European Association of Social Psychology and has published more than 100 scholarly articles on conflict resolution in organisations, group decision-making and creativity and innovation.

More recently, he has been exploring the role of the "love" hormone oxytocin in group dynamics and inter-group competition. His latest experiments, the results of which have been published in the Proceedings of the National Academy of Sciences, indicate a potentially more negative side.

Tell me about oxytocin.

It is a neurotransmitter and hormone produced in the hypothalamus known for its strong bonding function. It makes people more co-operative, benevolent, loyal, generous and trusting of others. It is involved in the parent-child bond - new mothers and fathers have raised levels of oxytocin. Production also increases when people hug and when they have sex and, recent research suggests, when they receive psychological warmth.

It is easy to see an evolutionary role in keeping couples and families together, but what about in groups?

Darwin talked about this - primitive societies in which members were co-operative and had a high level of altruism towards one another were more likely to survive. So the idea is, at the biological level, systems that facilitate and sustain group co-operation, such as oxytocin, are more likely to survive.

What sparked your interest in oxytocin?

I was reviewing the literature on human co-operation and saw studies showing that oxytocin makes people more generous and trusting. I started to wonder what co-operation means in the context of inter-group competition. Would co-operation, stimulated by oxytocin, be limited to your "in-group"?

What did you find?

We took groups of three and they had to play an economic game, competing with another group. They had money that they could a) keep for their personal benefit; b) invest in their in-group to their mutual benefit; or c) use to hurt the out-group. People given oxytocin increased their contributions to the in-group but there was no difference to their treatment of the out-group. The effect of oxytocin was limited to benefiting the in-group members.

Nepotism?

Exactly.

And your latest studies?

We asked whether oxytocin works on a more basic level, in influencing our views on people in the in-group and out-group. In one test, we got men of Dutch origin to judge people with typical Dutch, Arab and German names; in the Netherlands, a lot of immigrants and Germans are perceived as out-groups. We know that people tend to judge people from their in-group more positively than people from out-groups. In all five experiments, when we gave people oxytocin compared to a placebo, we found that people became much more positive about their in-group. In four experiments, the oxytocin had no effect on their evaluation of the out-group. In one, the people who had taken oxytocin became more negative about the out‑group also.

So this is the dark side of oxytocin?

When you give preferential treatment to your in-group as ethnocentrism, you implicitly indirectly discriminate against people who do not belong to your in-group. And they feel that, they feel resentment, they may protest, so indirectly, it could be that oxytocin contributes to inter-group tensions.

Could your work could have a practical application in addressing discrimination?

One of the longer-term practical implications is that we may be able to rethink where ethnocentrism comes from and what is causing it. Some scientists and societies think ethnocentrism is educative and [a result of] how the press writes about people. Our research shows that while that is partly true, there are these tendencies inherent within ourselves.

How adaptable is our idea of our in-group?

It is definitely possible to shift the boundaries. What oxytocin does is that once you see people as [belonging to your] in-group, you come to like them even more. Oxytocin doesn't make you a racist; it makes you like and commit to your in-group.

So you wouldn't see raised levels of oxytocin among racists?

No. It may contribute to ethnocentric attitudes but that doesn't mean that people who display ethnocentrism are driven by oxytocin. In the total absence of oxytocin you can still be ethnocentric.

What's next?

There are open questions still. In our studies, we sometimes found - but more often didn't find - that oxytocin creates an increased dislike of out-groups. So one question we are still working on is: are there specific features of an out-group that drive the effect of oxytocin towards disliking them? In the first set of experiments, we found that when people perceived the out-group as a threat to the in-group they became more competitive under oxytocin. Or is it that these findings were the result of coincidence and there is no effect?

It is fine-tuning, but it is important. We can see that it increases the love for your in-group but we are unclear whether it increases the hate for out-groups. If people are going to talk about the dark side of oxytocin, it is important as scientists that we can say: "We have looked at these findings and we have conclusions."