Theoria Generationis: the ancient roots of modern developmental biology

Abstract

The debate between to be and to become that opposed Parmenides and Heraclitus became converted, over the subsequent two millennia, into the dilemmas between preformation and epigenesis, and between immanence and transcendence. Aristotle, enunciating his Theoria generationis, moved the controversy from the realm of Metaphysics to Physics and can even be glimpsed trespassing into Biology in Harvey’s treatises De Motu Cordis and Exercitatione de Generatione Animalium which introduced the concept of ovism. In the same period, the spermatozoon (animalculum) was described, and ovism and animaculism became counterparts. The two theories could be read on the background of preformation or epigenesis. With the Enlightenment, the dispute over the processes of development was exposed to Cartesian rationalism and subjected to severe experimentation. Comte’s positivism led to the search for the material first causes of development, according to the laws of Physics and Chemistry, whereas Roux’s Entwicklungsmechanick ruled developmental biology during the nineteenth century until the middle of the last century when Crick and Watson published their research, finally resolving the millenary conflict between preformation and epigenesis in molecular and genetics terms.