Kill the competition: why siblings fight but colleagues cooperate

There is a certain rhythm to the swing of sibling relations. We resent our brothers and sisters in childhood. We support them in adulthood. We sue them after the reading of the will. The choreographer of this dance, as in so many others, is competition. When we lobby our parents for their affection and income, we make a claim on finite resources. And since our siblings also expect their cut, we inevitably come into conflict with them.

What is implicit in childhood and often made explicit in later adulthood, when the family estate is parcelled out and someone is unhappy with their lot, is that we are at those times in competition with our siblings above anyone else; people from other households are not entitled to our parents’ resources, and we are not entitled to theirs. In that long, happy period between childhood and the inheritance, however, we must vie instead for work and love with challengers from outside of our family. Competition between siblings thus relaxes, and our brothers and sisters become our friends, too.

We are more likely to share copies of our genes with blood relatives than with anyone else. This creates a shared interest in their success, because the production of nieces and nephews is simultaneously the reproduction of our genes. And so, over evolutionary time, genes that caused their bearers to care especially for their kin found their way into everything from microbes to plants and animals, including humans. Indeed, the American zoologist Richard Alexander, who died recently, once wrote that we ‘should have evolved to be exceedingly effective nepotists, and we should have evolved to be nothing else at all’. Consequently, siblings rarely kill each other. But when they do, the motive is usually competitive.

Read the whole story (subscription may be required): Aeon