 Classical ethology flourished in the years immediately following World War Two (Burkhardt 2005). At the same time others started to question the emphasis on environmental factors in behavioral development which had developed between the wars in the wake of the behaviorist revolution in psychology. Numerous lines of evidence suggested that psychology would have to take account of species-specific biological endowments if it was to understand how different species interact with their environment and the distinctive things each species is able to learn from these interactions (e.g. Harlow 1953; Tomkins 1962; Seligman 1970). By far the most influential criticism of behaviorism, however, came from linguistics. The linguist Noam Chomsky argued that existing behaviorist accounts of the development of language were unworkable and offered a general argument for the conclusion that the ability to acquire language is innate (Chomsky 1957; 1959; 1966). According to this ‘poverty of the stimulus’ argument, the examples of speech to which children are exposed do not contain enough evidence to settle which utterances are grammatical in the language they are trying to acquire. Nevertheless, children reliably acquire the grammar of their native language. Therefore, Chomsky and his followers concluded, children must have innate knowledge about grammar which supplements the evidence to which they are exposed during development. If this argument is sound, every normal childhood is a deprivation experiment that confirms the innateness of grammar. The details of the original poverty of the stimulus argument, its elaboration by Chomsky’s followers, and the current state of the evidence for linguistic nativism are discussed in detail in the entry  Innateness and Language.  What matters for current purposes is that Chomsky’s work produced a very broad consensus in psychology that language acquisition is explained by a complex, evolved mechanism that is present at birth and which can produce normal linguistic development in a wide range of environments, including those which are ‘impoverished’ with respect to language.