In this ground-breaking book, Johanna Nichols proposes means of describing, comparing, and interpreting linguistic diversity, both genetic and structural, providing the foundations for a theory of diversity based upon population science. This book will interest linguists, archaeologists, and population specialists. "e;An awe-inspiring book, unequalled in scope, originality, and the range of language data considered."e;-Anna Siewierska, Linguistics "e;Fascinating. . . . A brilliant pioneering study."e;-Journal of Indo-European Studies "e;A superbly reasoned book."e;-John A. C. Greppin, Times Literary Supplement