I have just finished reading Lenneberg’s 1967 seminal book The Biological Foundations of Language. It was, and still is, an incredibly insightful attempt to bring linguistics and biology closer together into what is currently called biolinguistics. It was also way ahead of its time in terms of the conceptual framework which underpins the biological theory of language proposed in the book. By amassing and integrating evidence from anatomy, neurology, cognitive science, evolutionary theory, developmental biology, child language acquisition, semantics, phonology and syntax, Lenneberg creates a theory of language based on a few far-reaching principles.
First, language is viewed as a species-specific behaviour. Every species is different in terms of how they develop and mature. To the extent that behaviour is based on neurophysiological properties of the organism and that neurophysiology is a product of species-specific paths of development and maturation, language can be considered a species-specific behaviour resulting from the human-specific ontogenetic process. Evidence for this includes well-documented and universal milestones in language development, sometimes even in the absence of appropriate linguistic stimuli.
Second, there does not appear to be any part of the brain dedicated to language. Certainly, there are regions of the brain (and particularly of the left hemisphere) which play a more significant role in language, but in general language is well-integrated into the cerebral structure as a whole. This makes it likely that language evolved from the outset as a complex integration of many parts; it is unlikely that the subcomponents of language evolved separately and only recently became unified.
Third, language structure exhibits evidence of three basic processes: (1) categorisation, (2) differentiation, and (3) transformation. Categorisation involves generalising over stimuli, i.e. creating an abstract representation. Differentiation involves splitting categories in various ways. Transformation involves being able to identify similarities between categories, i.e. being able to identify how one category is related to another in a systematic way. Lenneberg argues that these are cognitive skills which have been integrated into the structure of language. Furthermore, because every infant effectively creates language anew, these are the processes involved in language acquisition, for example, early child utterances go through a one-word stage, followed by a two-word stage, then simple sentences etc. This potentially shows differentiation in that one-word utterances are whole child sentences. As the child differentiates the earliest syntactic category into two (say, head and modifier), we begin to observe two-word utterances etc.
Fourth, environmental triggers are necessary for the proper actualisation of one’s innate potential for language. These triggers must be available during maturation otherwise the behaviour will not develop properly, i.e. there is a critical period for (first) language acquisition. The acquisition of language is thus a matter of nature and nurture, innateness and learning.
There are other principles which Lenneberg summarises in the final chapter, but these give a flavour of the framework in which his theory is set. Language is at its foundations a biological phenomenon, and biolinguistics can help us formulate and pursue questions to understand it in a more insightful and informed way.