The judge plays an important role in Hayek’s theory of cultural evolution. He argues that the universal rules of just conduct could only evolve in legal systems in which it was the task of judges to “discover” the appropriate rules. This article scrutinizes Hayek’s optimistic view on the judicial “shaping of the rule”. It asks, whether the beneficial effects of judge made law are indeed as generally to be expected as Hayek presented it. The analysis follows Hayek’s own methodological guidelines, which are depicted at the beginning. The following portrayal of the theory of cultural evolution puts special emphasis on the judge’s contribution to legal development. Hayek’s theory in general has been criticized along two lines: on the one hand, it was argued that the processes and the criteria of selection remain vague. On the other hand, it was stressed that an evolutionary process can only be expected to lead to beneficial outcomes under certain conditions, which ought to be specified. I argue that also adjudication, seen as a mechanism in legal evolution, is not beneficial as such. As an example I present a part of German Competion Law. This example is chosen, because it is directly related to the spontaneous order of markets and because the statute only gives some guidelines for “fair” competition. Thus, like in common law systems, judge-made law is extremly important. This example can show that, in contrast to Hayek’s unconditional statement about judge-made law, adjudication can result in serious distortions of a spontaneous order. From the perspective of legal philosophy I argue, that Hayek rejects legal positivism only with respect to the legislator, in not accepting each formally correct enacted statute as law. Conceptualizing any formally correct judicial decision as a valuable contributions to cultural evolution, however, is only another kind of positivism. Finally, Jhering’s early contibution to a theory of legal evolution is presented as a promising approach that could complement Hayek’s theory of cultural evolution.