This introduction presents an overview of key concepts discussed in the book. The book addresses central issues in the domain of language development: the range of evidence in favor of a language instinct, the existence of a critical period for language acquisition, the issue of maturation in the context of language acquisition, and the impact of language on other cognitive systems. It focuses on the interplay between mind, brain, and behavior. The book deals with the nature of theoretically informed experiments, working memory and language processing, modularity, language deficits, and pathologies. It focuses on a range of issues relevant to the study of language evolution: the cognitive capacities of non-human primates, the abilities of non-human vocal learners, the potential use of fossil records to shed light on the evolution of language, the possible role of natural selection, and the insights from computational modeling in the context of language evolution.

This chapter considers two competing views about what modularity might consist of, which the authors refer to as sui generis modularity and descent-with-modification modularity. Descent-with-modification helps make sense of the considerable phylogenetic continuity that has been documented in recent years, in terms of comparative psychology, comparative neuroanatomy, and comparative genomics. The chapter also considers language, the canonical putative module, and its relation to cognitive systems. Cognitive mechanisms for spatial and temporal representation seem to run deeply through the structure of the linguistic system. The notion of descent-with-modification, once recognized, has significant implications for how one can assesses debates about modularity. The descent-with-modification perspective suggests caution for inferring the absence of modularity from many studies of "normal" cognition. Descent-with-modification also suggests that one should expect the hallmarks of ancestry even in the very machinery that makes abstract linguistic representation possible.