This book offers a new approach to language change, the punctuated equilibrium model. This is based on the premise that during most of the 100,000 or more years that humans have had language, states of equilibrium have existed during which linguistic features diffused across the languages in a given area so that they gradually converged on a common prototype. From time to time, the state of equilibrium would be punctuated, with expansion and split of peoples and of languages. Most recently, as a result of European colonization and the globalization of communication, many languages currently spoken face imminent extinction. Professor Dixon suggests that every linguist should assume a responsibility for documenting some of these languages before they disappear.

Professor Dixon argues that the commonly used family tree model of language change is appropriate during a period of punctuation, but not during the longer periods of equilibrium. He suggests that many of the views currently held by linguists, archaeologists and geneticists need serious rethinking, and emphatically dismisses recent speculation that the original languages of humankind could be reconstructed.