The Biology of Suicide Bombers

Primatologist Eric Michael Johnson has a fascinating post about why suicide bombing s a uniquely human problem. It appears that while altruism may be found in other animals, spite is a uniquely human characteristic:

Someone walks into a crowded restaurant, looks about the diners calmly, and blows themselves up as well as everyone nearby. Why? This is a scenario that forces us to explain the dark side of human nature. Why do humans have a capacity for such hate that they’ll take their own lives in order to destroy others?

A recent study on chimpanzee behavior suggests that humans may be alone in this way: a dubious distinction to say the least. In a review published yesterday in the Chicago Tribune the researchers suggest:

"Spitefulness may be a peculiarly human trait," said Keith Jensen, a Canadian evolutionary biologist who has been looking to see whether human concepts like fairness and punishment are present in the social organization of another highly socialized species.

In biological terms spite is the flip side to altruism and both have posed a thorny issue for evolutionary biologists. While an altruistic act is one where the actor takes a hit in order to help someone else, a spiteful act is one where that same actor seeks to hurt someone else at a cost to themselves.

"Spite is kind of interesting, because it is altruism's evil twin," Jensen said. "Humans can care about making somebody feel better, but we also have the darker side of sometimes wanting to make somebody feel worse."

W.D. Hamilton, the British evolutionary biologist most famous for kin selection theory, proposed how altruism could evolve in a population composed of close relations. If the cost to the actor is less than the benefit to the recipient times their coefficient of genetic relatedness (0.5 for full siblings, 0.25 for nephews) than the altruistic act improves their inclusive fitness and the trait will perpetuate.

Hamilton also wrote on altruism’s evil twin in his classic 1970 Nature paper “Selfish and Spiteful Behaviour in an Evolutionary Model”. Hamilton suggested that the evolution of spiteful behavior could be selected for in cases where the recipient of the spite was less likely to be related than an average member of their population. This is because, if a spiteful organism goes out of their way to hurt someone related to them, those spiteful genes would be less likely to be passed on by both the individual and the recipient of the spite. However, if that same organism were to sacrifice themselves to hurt someone less related than the rest of the population it could benefit their inclusive fitness.

Read it all here.