Media type: E-Article Title: Genetic Variation and Progressive Evolution Contributor: Layzer, David imprint: University of Chicago Press, 1980 Published in: The American Naturalist Language: English DOI: 10.1086/283602 ISSN: 0003-0147; 1537-5323 Keywords: Ecology, Evolution, Behavior and Systematics Origination: Footnote: Access State: Open Access