"Differentiation of populations" (1969) Science: 165 pp 1228-1232
Ehrlich, P.R. & Raven, P.H.
Copyright (1969) American Association for the Advancement of Science.
A stimulating, influential but by no means universally endorsed critique of the idea that gene flow is the main factor responsible for maintaining species. It is of great importance to the species concept debate and a strong argument for the ecological as opposed to the biological species concept.