We revisit the question of price formation in general equilibrium theory. We explore whether evolutionary forces lead to Walrasian equilibrium in the context of a market game, introduced by Shubik (1972). Market games have Pareto inferior (strict) Nash equilibria, in which some, and possibly all, markets are closed. We introduce a strong version of evolutionary stable strategies (SESS) for finite populations. Our concept requires stability against multiple, simultaneous mutations. We show that the introduction of a small number of ``trading mutants'' is sufficient for Pareto improving trade to be generated. Provided that agents lack market power, Nash equilibria corresponding to approximate Walrasian equilibria constitute the only approximate SESS.