Bacteria That Cheat, and the Kings We're Built to Catch

Wherever real cooperation exists, cheating exists right alongside it. Some of the clearest proof of that comes from an organism with no brain at all.

When Bacteria Build a Tower Together

Certain bacteria live alone for most of their lives, but when it is time to reproduce, they gather together and build a structure called a fruiting body: a stalk holding up a top section. Only the bacteria in the top section get to release new cells. The bacteria that end up forming the stalk sacrifice their own reproduction so the ones on top can reproduce.

In a fair system, two strains share this cost equally, taking turns being stalk and top in roughly equal numbers. Cheating looks like one strain rushing to grab the top position for itself, forcing the other strain to always be the stalk.

Bacteria have a defense against this. Strains that get cheated can change the docking proteins on their surface so they only bind to their own strain, physically excluding the cheater from the group next time. A single-celled organism with no brain has evolved a working system for detecting cheaters and refusing to cooperate with them again.

Humans Are Built to Spot This Too

Psychologists have found the same instinct, sharpened, in humans. In one classic experiment, people are told a story about a king who promises a reward for a completed task and threatens punishment for failure. The listener has to work out whether justice was served at the end.

There are two ways the story can go wrong: the king punishes someone who actually succeeded, or the king rewards someone who actually failed. People are dramatically better at noticing the first kind of injustice, someone being cheated out of an earned reward, than the second kind, someone getting an unearned reward. Chimpanzees show the same bias: they notice a cheater far more readily than they notice someone being needlessly generous.

The Theory, and the Man Who Got There First

The formal theory behind all of this, reciprocal altruism, came together in the 1970s through the work of Robert Trivers. Before Trivers, the standard view of evolution was almost entirely about competition, domination, and aggression. His work showed that cooperation could be just as much a product of natural selection as conflict was.

It was treated as revolutionary. It had already been said, in full, about 80 years earlier. A Russian scientist named Peter Kropotkin, born a prince and later a committed anarchist who was jailed repeatedly for his politics, published a book called "Mutual Aid: A Factor of Evolution" long before mainstream biology caught up. When the Russian Revolution finally arrived, Kropotkin was close to Lenin's circle, but because he was an anarchist and not a loyal party member, Lenin reportedly plotted to have him killed. By then Kropotkin was already dying of old age, so the plan was quietly dropped. Kropotkin argued that cooperation, not just struggle, could be a real force in evolution, and the rest of the field only arrived at the same conclusion decades later.

Knowing that cooperation can evolve is one thing. The much harder question, the one that occupied game theorists and zoologists alike, is figuring out exactly when an individual should cooperate and when it should cheat.

Further Reading

• Book: Mutual Aid: A Factor of Evolution by Peter Kropotkin, the book that predicted this entire field decades early.
• Wikipedia: Robert Trivers · Peter Kropotkin · Cheating (biology)