In this paper I argue that semiotic cognition is a distinctive form of cognition, which must have evolved out of earlier forms of non-semiotic cognition. Semiotic cognition depends on the use of signs. Signs are understood in terms of a specific organization, or structure, of the cognitive process. Semiotic cognition is a unique form of cognition. Once this form of cognition was available to humans, the semiotic provided the ground structure for an evolutionary development that was no longer strictly Darwinian, but followed its own semiotic logic. In the increasingly abstract ways in which the ubiquitous difference is dealt with, we discover this logic of cultural evolution, which determines the course of long term cultural change.