Abstract

Although developmental biology is an institutionalized discipline, no unambiguous account of what development is and when it stops has so far been provided. In this article, I focus on two sets of developmental molecular mechanisms, namely those underlying the heterochronic pathway in C. elegans and those involving Hox genes in vertebrates, to suggest a conceptual account of animal development. I point out that, in these animals, the early stages of life exhibit salient mechanistic features, in particular in the way mechanisms of genetic regulation occur in the organism. Indeed, these stages are characterized by sequential and irreversible changes in gene expression taking place throughout the organism. A general definition of animal development based on these distinctive features implies that, at least for some animal species, development does not go on throughout the life of the animal, contrary to what has recently been claimed by some biologists and philosophers. Instead, in such species, development encompasses various events occurring sequentially at the beginning of life.