Abstract

Historians have emphasized the appearance of a productive research program in genetics after 1910, and philosophers and biologists have considered endorsement of genetics as a progressive move, indeed as a starting point for modern experimental biology. These efforts focus on what biology had changed to. This paper examines the condition from which biology moved, stressing the way in which Americans held heredity and development as a natural, intimately intertwined couple. Heredity accounts for likenesses, development for variation, and the two act together throughout an individual's life. This discussion establishes the antecedent conditions necessary to explain the split of genetics and embryology and addresses the reasons for the split