We discuss how small group interactions overcome evolutionary problems that might otherwise erode vengefulness as a … traits. We show how within-group social norms can solve these problems even when encounters with outsiders are also important. …

from a laboratory experiment in which subjects choose their group membership, which is interpreted as decision to identify … with the respective group. Inducing a trade-off between monetary payoffs and different group identification choices we … individual out-group discrimination in allocation decisions, which has previously been shown to be associated with social …