Two-person cooperation

aka social exchange, reciprocation, reciprocal altruism

For years, we have worked on how people reason about social exchange: How they represent agreements to exchange, what inferences they make, and mechanism specialize for detecting cheaters. That research is discussed on the page, Reasoning about Social Exchange.

Scientists at the CEP also study motivations and behavior in dyadic cooperation.

Behavioral ecology and cooperation

The CEP’s Michael Gurven has studied the behavioral ecology of social exchange in small-scale hunter-gatherer and hunter-horticulturalist societies. Here is his classic target article in Behavioral and Brain Sciences, To give and to give not: The behavioral ecology of food transfers. He and Adrian Jaeggi have been testing alternative models of cooperation, comparing humans to other primates. See, e.g., their paper examining reciprocity versus kin selection phylogenetically, and their comparative work on food sharing, Natural Cooperators. reciprocity versus kin selection. You will find a wealth of relevant information by browsing his website.

Partner choice models of cooperation

During the 1990s, evolutionary scientists introduced models of the evolution of cooperation in biological markets: situations in which you can switch cooperative partners and they can leave you for better alternatives. These are called partner choice models.

When partner choice is possible, two problems arise: figuring out who would be a valuable cooperative partner, and cultivating a reputation that will make valuable partners want to choose you. Sakura Arai has been studying how partner choice has shaped motivations to reciprocate cooperation and sanction defections.

How does sanctioning affect your reputation? When engaging in dyadic cooperation, what happens when someone defects—that is, fails to reciprocate? You could do nothing, withdraw cooperation, or inflict punishment (either restorative or costly). Sakura Arai wanted to know how each of these responses affects your (various) reputations (e.g., as cooperative, vindictive, exploitable, etc). See:

Arai, Sakura, Tooby, John, & Leda Cosmides (2023) Why punish cheaters? Those who withdraw cooperation enjoy better reputations than punishers, but both are viewed as difficult to exploit. Evolution and Human Behavior 44, 50-59.

For a brief account, see her blog post on the Human Behavior and Evolution Society website.

Does the degree of partner choice in your local social ecology calibrate your motivations to reciprocate and sanction defections? The answer is yes—even in the lab, when you know you are interacting with strangers! See:

Arai, S., Tooby, J., & Cosmides, L. (2022). Motivations to reciprocate cooperation and punish defection are calibrated by estimates of how easily others can switch partners. PLoS One, 17(4), e0267153. 

Is generosity in one-shot interactions irrational? Click here to find out!