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A new look at the evolution of spite

Medea about to kill her children, by Eugene Delacroix, 1838 (Louvre, Paris). Biologists are investigating the evolution of a seemingly irrational behavior, spite.

Spite is not only an enduring theme of literature and theater – it has also been a scientific conundrum for decades. Evolutionary biologists have been unable to explain how or why evolution would have generated this form of behavior, one of humanity’s most common and distinctive tendencies.

The puzzle is rooted in the generally accepted view that evolution is a force that promotes the spread of the genes best suited to help organisms survive. If this is true, biologists have wondered, why would evolution allow such a costly behavior as spite to establish itself?

But two researchers think they may have an answer.

The pair of University of Cambridge, U.K. zoologists say spiteful actions may actually benefit their perpetrator, by communicating an important signal to whomever might be nearby. The signal is that the perpetrator is willing to go very far – perhaps unreasonably far – to punish those who cross him or her. Although such a signal is costly to send out in the short run, it might more than pay for itself in the long run by discouraging others from attacking the perpetrator.

Spite, in short, is a sort of advertisement. If this view is correct, examples of spiteful behavior among non-human animals might start coming to light, say the researchers, Rufus Johnstone and Redouan Bshary. They make the argument in a paper in the September issue of the research journal Proceedings of the Royal Society of London B.

Johnstone and Bshary concede in their paper that there have been few or no reports of spiteful behavior among animals. “We suggest, however, that spiteful aggression has often been overlooked,” they add. Anytime an animal attacks another and loses the fight, they explain, an explanation to be considered is spite. In other words, the aggressor may have attacked without any particular expectation of winning, but simply to advertise that he or she is not one to be trifled with.

Spiteful aggression may have a second evolutionary purpose, Johnstone and Bshary add: it could enhance an animal’s attractiveness to potential mates “because it serves as a signal of strength.” By acting spitefully, an animal sends a signal to potential mates that it is tough enough to afford losses and even injuries.

In suggesting this solution to the puzzle of the evolution of spite, Johnstone and Bshary say, they have borrowed a page from past researchers who have offered a mirror-image solution to another evolutionary quandary.

This other puzzle is how altruism evolved. This question has thrown evolutionary biologists into a confusion similar to that which surrounds the spite question; in fact, the debate over the altruism issue has a much longer and deeper history. The basic question is similar. Altruism is a seemingly costly trait; by definition, the altruist gives, and gets little or nothing in return. How could evolution allow such a trait to survive?

Some theorists have shown that in certain environments, altruism can establish itself in evolution as, again, a sort of advertisement. The altruist enhances his or her reputation so that others are willing to help him or her in a time of need. Moreover, the altruist scores points with potential mates, because his or her generous actions are a signal that he or she is strong enough to afford them.

It hasn’t escaped researchers’ notice that both evolutionary puzzles have striking similarities, despite the fact that they deal with seemingly opposite traits. Some researchers have even described spite as altruism’s “evil twin.”

—EJL

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