There is a remarkable resonance between recent findings about medical malpractice litigation and theories about the evolution of co-operation and reciprocity among humans. This should not be altogether surprising: theories of reciprocity seek to explain the behaviours we exhibit when we interact to punish or confer benefits on each other; while civil liability litigation may be just one of modern society’s ways of compelling otherwise unrequited reciprocity. The link between the two fields of study is worth exploring nonetheless. Just as behavioural economics and evolutionary theory offer useful insights for those of us who study legal phenomena, data about the behaviour of people accessing legal institutions may be useful to those who build behavioral theories. This essay is therefore, in a way, a lawyer’s effort to return the favour.