ontogénesis

Ontogenesis, or the developmental biology of an individual, refers to the sequence of changes that an organism undergoes from its formation to its mature state and through later life. The term derives from Greek ont- “being” and genesis “origin.” Ontogeny encompasses embryonic development, post-embryonic growth, maturation, and aging, including cellular differentiation, tissue and organ formation, and the regulated patterns of growth that arise from gene expression and cellular signaling, interacting with the environment. It describes how an organism becomes structurally and functionally competent to survive and reproduce.

Ontogenesis is distinguished from phylogenesis, the evolutionary development of species across generations. Key concepts include epigenesis, the emergence of form during development, and the role of genetic and epigenetic regulation in shaping developmental trajectories. Environmental factors such as nutrition, temperature, and stress contribute to phenotypic plasticity, influencing timing and outcomes. Development proceeds through phases such as fertilization, cleavage, gastrulation, organogenesis, and growth, followed by maturation and, in many species, metamorphosis or aging. Research spans embryology, molecular and developmental genetics, and regenerative medicine, with applications in understanding congenital anomalies, stem cell therapies, and tissue engineering. Although the historical idea that ontogeny recapitulates phylogeny is now rejected, modern development biology emphasizes lineage-specific, dynamic processes that produce a single, functioning organism.