The paper presents an evolutionary model illustrating the dynamics that give rise to discriminatory social norms i.e. such rules of behaviour that fulfi l two conditions: (1) they treat differently actors having the same abilities and technical options, but differing in some arbitrary sense (2) they are supported by socially enforced sanctions. In the presented model both discrimination and social norms are necessary to solve a coordination problem that arises when the situation requires different actors to perform different tasks. The properties of behavioural rules relying on discrimination and leading to various degrees of inequality are analysed. It is demonstrated that in general norms ensuring equal payoffs are easier to stabilize, but unfair norms can also be stable.