In fact, as Descartes himself quite correctly observed, language is a species-specific human possession, and even at low levels of intelligence, at pathological levels, we find a command of language that is totally unattainable by an ape that may, in other respects, surpass a human imbecile in problem-solving ability and other adaptive behavior. Language and Mind (1968)
The child must acquire a generative grammar of his language on the basis of a fairly restricted amount of evidence. To account for this achievement, we must postulate a sufficiently rich internal structure – a sufficiently restricted theory of universal grammar that constitutes his contribution to language acquisition. Language and Mind (1968)