Rock, Paper, Scissors Is Not Cooperation

Green beard cooperation only needs one shared signal. The third and strangest strategy, reciprocal altruism, needs no shared signal and no shared genes at all, just two individuals who both benefit from working together.

A Bacterial Standoff That Looks Like Peace

The scientist Brendan Bohannon studied three strains of E. coli bacteria and found something that looked, at first, like a beautiful example of restraint in nature.

• Strain one makes a poison that kills other strains, but making the poison is costly for strain one itself.
• Strain two is hurt by the poison, but is excellent at gathering food.
• Strain three is immune to the poison, but is bad at gathering food.

Put all three strains near each other, and they form a cycle: the poison-maker beats the food-gatherer, the food-gatherer out-competes the immune strain for food, and the immune strain survives the poison that would kill the food-gatherer. Each strain can dominate one rival but loses to the other.

This is not cooperation. It only looks like restraint because going all-in against one rival lets the third strain flourish and eventually turn the tables. It is closer to nuclear deterrence than to peace: nobody wants total war, not because they love their neighbor, but because total war backfires on them personally.

What Real Cooperation Requires

Actual reciprocal altruism is rarer and more specific: you help another individual, and you do it because there's a real chance they will help you back. This shows up far beyond bacteria.

Even viruses do it. In a field researchers call sociovirology, one viral strain that is excellent at entering a cell can drag a second strain in with it, while that second strain is excellent at bursting the cell open once it's full of new virus copies. Neither strain is smart, social, or capable of recognizing kin, and they still end up working as a team because it benefits both of them.

Among animals with real memory and social bonds, the logic is even more direct. Rhesus monkeys that hunt cooperatively end up with more food per individual than monkeys hunting alone. The same is true of human hunter-gatherers: teaming up on a hunt reliably produces more food per person than everyone hunting solo.

Once cooperation like this exists, though, a new temptation appears immediately: if you can find a partner who cooperates, the biggest possible payoff comes from taking their help while quietly giving nothing back. That single incentive to cheat, and the incentive to catch cheaters, turns out to shape an enormous amount of social behavior across very different species.

Further Reading

• Book: Behave: The Biology of Humans at Our Best and Worst by Robert Sapolsky, which covers reciprocal altruism in more depth.
• Wikipedia: Reciprocal altruism · Rock paper scissors (game theory)