Ontogeny (also ontogenesis or morphogenesis) is the origination and development of an organism, usually from the time of fertilization of the egg to the organism’s mature form. Yet, the term can be used to refer to the study of the entirety of an organism’s lifespan.
Ontogeny pertains to the developmental history of an organism within its own lifetime, as distinct from phylogeny, which refers to the evolutionary history of a species. In practice, writers on evolution often speak of species as “developing” traits or characteristics. This can be misleading. While developmental (i.e., ontogenetic) processes can influence subsequent evolutionary (e.g., phylogenetic) processes (see evolutionary developmental biology), individual organisms develop (ontogeny), while species evolve (phylogeny).
Ontogeny, embryology and developmental biology are closely related studies and the terms are sometimes used interchangeably. Recently (2003), the term ontogeny has been used in cell biology to describe the development of variouscell types within an organism.