This book puts forward a different 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 colonisation and the globalisation of communication which are likely to result in the extinction, within the next hundred years, of 90% of the languages currently spoken. Professor Dixon suggests that every linguist should assume a responsibility for documenting some of these languages before they disappear.