Contents

06 April 2007
Vol 316, Issue 5821

About The Cover

Cover image expansion

COVER A Chihuahua walking with a Great Dane more than 50 times its mass. The extreme diversity in body size among purebred dogs is greater than that of any other mammalian species. Researchers have identified a gene that helps explain this size diversity. See page 112 . Photo: Deanne Fitzmaurice