This book explores the development of creoles and other new languages, highlighting conceptual and methodological issues for genetic linguistics and discussing the significance of ecologies that influence language evolution. It presents examples of changes in the structure, function, and vitality of languages, suggesting that similar ecologies have played similar roles in all cases of language evolution. Using theories of language formation, macroecology, and population genetics, it proposes a common approach to creole and other new language development. Eight chapters discuss the following: (1) "Introduction" (e.g., pidgins, creoles, and koines); (2) "The Founder Principle in the Development of Creoles"; (3) "The Development of American Englishes: Factoring Contact in and the Social Bias Out" (e.g., the development of African American English and white English vernaculars); (4) "The Legitimate and Illegitimate Offspring of English" (e.g., mutual intelligibility); (5) "What Research on the Development of Creoles Can Contribute to Genetic Linguistics" (e.g., creolization as a social process); (6) "Language Contact, Evolution, and Death: How Ecology Rolls the Dice"; (7) "Past and Recent Population Movements in Africa: Their Impact on its Linguistic Landscape" (e.g., the linguistic impact of European colonization); and (8) "Conclusion: The Big Picture." (Contains approximately 400 references.) (SM)