Ontogenesen

Ontogenesen, or ontogeny in English, is the developmental history of an individual organism from fertilization or birth to adulthood, including growth, differentiation, and maturation. The term derives from Greek roots meaning “being” and “origin.” In biology, ontogeny encompasses embryonic development, post-embryonic growth, and aging, with variations such as metamorphosis in some taxa.

During embryonic development, organisms undergo processes such as cleavage, gastrulation, and organogenesis, establishing the body plan and differentiating tissues and organs. Post-embryonic development covers growth to reproductive maturity, changes in form and function after birth or hatching, and, in many species, senescence. Some lineages exhibit dramatic transformations, such as metamorphosis, while others show gradual or indeterminate growth.

The courses of ontogeny are governed by genetic programs that regulate gene expression and cell signaling, as well as epigenetic mechanisms that modulate gene activity without altering DNA sequence. Environmental factors—including nutrition, hormones, temperature, and social context—can influence timing and outcomes, contributing to developmental plasticity and variation. Concepts such as heterochrony describe shifts in the timing of developmental events that can drive evolutionary change, while allometry concerns how different body parts grow at different rates.

Researchers study ontogeny using a range of model organisms and techniques, including lineage tracing, live imaging, and molecular profiling, to understand how form and function emerge. Understanding ontogeny informs fields from developmental biology and embryology to medicine, evolutionary biology, and ecology.

See also: Ontogeny, Embryology, Developmental biology, Metamorphosis, Aging.