Racial and ethnic divisions, sometimes flairing into hatred, sometimes even into genocide, are part and parcl of human life. However evil and damaging such activity is, it is by no means rare in the course of human history. From the Israeli/Palestinian conflict to Rwanda, from Northern Ireland to inner-city America, from Nazi Germany to today's polarization between Muslims and the West, throw in football hooligans if you like, we're a species marked by our tendency to form "in groups" and "out groups" based on crude markers -- from skin colour and religion to nationality, jersey colour or the kind of handbag you carry. Our habits of unthinking discrimination seem like a horrible flaw in human nature -- something that sadly prevents our higher rational and cooperative character from flowering.

But scientists increasingly suspect that there may be no "flaw", and that there's a perfectly natural explanation for why we act like this. Evidence ranging from psychological experiments to mathematical theory suggests that individuals can actually benefit by being crudely discriminatory; that groups, being acting on crude prejudice, can create more cooperation among themselves than otherwise. Our uglier habits today may reflect core behaviours that helped our ancestors survive -- and in some settings today, still offers individual benefits, despite their raw conflict with accepted principles of human decency.

So we may be "hard-wired" to be prejudiced. If so, this may offer little encouragement for those trying to make a practical difference in the world's trouble spots, from Iraq to Darfur. But researchers also believe that facing up to the truth of our own nature may be the best way to learn how to engineer our collective lives around it. With careful planning, it may be use human psychology to our advantage -- and take some of the awful energy out of ethnic and racial tensions.

This article will appear within the next few weeks in New Scientist.