Cost-effective external interference for promoting the evolution of cooperation.

The problem of promoting the evolution of cooperative behaviour within populations of selfregardingindividuals has been intensively investigated across diverse fields of behavioural, socialand computational sciences. In most studies, cooperation is assumed to emerge from thecombined actions of participating individuals within the populations, without taking into accountthe possibility of external interference and how it can be performed in a cost-efficient way.Here, we bridge this gap by studying a cost-efficient interference model based on evolutionarygame theory, where an exogenous decision-maker aims to ensure high levels of cooperationfrom a population of individuals playing the one-shot Prisoner’s Dilemma, at a minimal cost.We derive analytical conditions for which an interference scheme or strategy can guarantee agiven level of cooperation while at the same time minimising the total cost of investment (forrewarding cooperative behaviours), and show that the results are highly sensitive to the intensityof selection by interference. Interestingly, we show that a simple class of interference thatmakes investment decisions based on the population composition can lead to significantly morecost-efficient outcomes than standard institutional incentive strategies, especially in the case ofweak selection