Microfinance is an economic development intervention that involves credit provision to low-income entrepreneurs in order to stimulate economic growth and reduce poverty. Lenders typically require joint liability, where borrowers share the responsibility of repaying a group loan. We argue that this lending practice is subject to a fundamental cooperation problem similar to that faced by humans and other organisms in nature across many domains, and that consequently evolutionary theories of cooperation from the biological sciences can provide new insights into loan repayment behaviour. This could both inform the design of microfinance institutions, and offer a real-world test case for evolutionary theories of cooperation. We first formulate hypotheses on group loan repayment based on the evolutionary literature on cooperation. We then assess these hypotheses by reviewing 40 studies on micro-borrowers’ loan repayment from 31 countries, evaluating which characteristics of borrowers are associated with credit repayment discipline. We find more supportive than contrary evidence for the hypotheses, but results are generally mixed, generating avenues for future research within this framework. Our work shows how understanding the evolution of cooperation can guide economic development interventions that build on “social capital” and, more generally, offer ultimate explanatory theories for phenomena studied by social scientists.