This essay argues that there can be a duty to obey the law when it is produced by the evolutionary forces at work in the customary and common law. Human beings’ inherent epistemic limitations mean that they must rely on the trial and error learning built into the common law process to discover rules that facilitate peaceful social interaction. Hence, a duty to obey the law produced by the common law process can arise from individuals’ natural duty to promote social peace. This argument cannot be extended to ground political obligation. It does not give rise to a duty to obey the state.