(Paperback)

Explores the origins and development of geographic variation, divergence, and speciation. This work shows how geographic differentiation and speciation may develop in spite of continuous gene flow. It discusses the relationships among gene flow, dispersal, and migration.

(Paperback)

Discusses the methods and problems involved in the demonstration and measurement of natural selection. This work presents the critical evidence for its existence, and places it in an evolutionary perspective. It argues that natural selection can explain the change of frequencies of variants, but not their origins.