Structurally, cognitive and biological evolution are highly similar. Random variation and constant but blind selection drive evolution within biology as well as within cognition. However, evolution of cognitive programs, and in particular of grammar systems, is not a subclass of biological evolution but a domain of its own. The abstract evolutionary principles, however, are akin in cognitive and biological evolution. In other words, insights gained in the biological domain can be cautiously applied to the cognitive domain. This paper claims that (...) the cognitively encapsulated, i.e. consciously inaccessible, aspects of grammars as cognitively represented systems, that is, the procedural and structural parts of grammars, are subject to, and results of, Darwinian evolution, applying to a domain-specific cognitive program. Other, consciously accessible aspects of language do not fall under Darwinian evolutionary principles, but are mostly instances of social changes. (shrink)