The Evolutionary Psychology of Breaking Informal Versus Formal Contracts: Effects of Group Size and Area of Upbringing.

The social context for human social interactions between modern urban contexts and ancestral, small-scale contexts is different in many important ways. Before the advent of agriculture, all people lived in small-scale social contexts and were surrounded by kin and other familiar others. As these conditions characterized the lion's share of human evolutionary history, we can expect much of our social psychology to be more designed for such small-scale contexts than for large-scale contexts. The study described here specifically predicted that informal forms of making an agreement (such as a handshake, which is more similar to how contracts are sealed in small-scale societies) would be weighted more heavily by people who are given an option to break a contract in a small-scale context. On the other hand, we predicted that people who are framed to think about large-scale social contexts will give more weight to written contracts. Using a 2*2 between-groups design (with 200 young adult participants), this interaction-based hypothesis was supported. We also found that, apart from experimental conditions, participants who reported coming from urban backgrounds were more likely to break a deal of any kind relative to others. Implications for cultivating prosocial outcomes against this backdrop are discussed.