Warfare induces post-marital residence change

Post-marital residence is a sex-biased dispersal defined by the place where a newly-wed couple lives after marriage. Common choices for this practice include patrilocal residence, where the couple lives with the man's family, and matrilocal residence, where they live with the woman's family. Deviations from accepted practice typically invoke strong sanctions, but despite this pressure to conform to post-marital residence norms, residence states are unexpectedly dynamic over time. Theories have been proposed to explain the pressures, both internal and external, that drive these changes in post-marital residence state. Two of the most popular emphasize the importance of warfare, but are largely restricted to qualitative statements. Here, we develop an agent-based model that captures key features of these theories, with a particular focus on warfare. We show that warfare can change post-marital residence practices, but such change only propagates through a wider network of communities under a narrow set of conditions. Additional factors, potentially including a strong sex-bias in the division of labor, are required to induce change more widely. While warfare thus serves as an important trigger for residence change, multiple interacting forces appear to be necessary to shift communities between different post-marital residence states under most conditions.