Ontogeny

Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development^[1]), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the study of the entirety of an organism's lifespan.

Ontogeny is the developmental history of an organism within its own lifetime, as distinct from phylogeny, which refers to the evolutionary history of a species. Another way to think of ontogeny is that it is the process of an organism going through all of the developmental stages over its lifetime. The developmental history includes all the developmental events that occur during the existence of an organism, beginning with the changes in the egg at the time of fertilization and events from the time of birth or hatching and afterward (i.e., growth, remolding of body shape, development of secondary sexual characteristics, etc.).^[2] While developmental (i.e., ontogenetic) processes can influence subsequent evolutionary (e.g., phylogenetic) processes^[3] (see evolutionary developmental biology and recapitulation theory), individual organisms develop (ontogeny), while species evolve (phylogeny).

Ontogeny, embryology and developmental biology are closely related studies and those terms are sometimes used interchangeably. Aspects of ontogeny are morphogenesis, the development of form and shape of an organism; tissue growth; and cellular differentiation. The term ontogeny has also been used in cell biology to describe the development of various cell types within an organism.^[4] Ontogeny is a useful field of study in many disciplines, including developmental biology, cell biology, genetics, developmental psychology, developmental cognitive neuroscience, and developmental psychobiology. Ontogeny is used in anthropology as "the process through which each of us embodies the history of our own making".^[5]