ontogeny

Ontogeny is the development of an individual organism from the zygote to its mature form. The term comes from Greek roots meaning being and origin. In biology, ontogeny is often discussed in relation to phylogeny, the evolutionary history of a species, with ontogeny focusing on the individual life cycle.

Ontogeny encompasses embryology, post-embryonic development, growth, differentiation, morphogenesis, and aging. Development is governed by genetic programs that are expressed through cellular signals and are influenced by environmental factors such as nutrition, temperature, and hormones. In many organisms, development begins with embryogenesis, a series of regulated cell divisions and pattern formation, followed by growth and maturation.

Patterns of development vary across taxa. Some species exhibit direct development, emerging as a miniature version of the adult, while others undergo indirect development with larval stages or metamorphosis (as in many insects and amphibians). Heterochrony describes shifts in the timing of developmental events that can drive evolutionary change, and neoteny refers to the retention of juvenile traits in the adult form.

In humans, ontogeny includes prenatal stages (zygote, embryo, fetus), postnatal growth, and puberty, with hormonal regulation shaping maturation. Aging is often considered part of the extended ontogenetic process.

Ontogeny is a central concept in biology and medicine, informing studies of development, variation, and evolution. It is investigated using model organisms and modern developmental techniques, helping to illuminate how genetic, cellular, and environmental factors shape the course of an organism’s life. The once-popular notion that ontogeny recapitulates phylogeny is now viewed as oversimplified, though development continues to influence evolutionary trajectories.