This book examines five central issues of second language acquisition: transfer, staged development, cross-learner systematicity, incompleteness and variability. It is argued that the first four of the five central issues receive a more satisfactory account than has been previously provided through an approach based on universal grammar. The fifth - variability - requires an account based on requirements of language use and language processing.
Motoo Kimura, as founder of the neutral theory, is uniquely placed to write this book. He first proposed the theory in 1968 to explain the unexpectedly high rate of evolutionary change and very large amount of intraspecific variability at the molecular level that had been uncovered by new techniques in molecular biology.