‘Epi’ means something upon or addition to. Thus, development of structures and functions is not determined solely by the ‘unfolding’ of instructions in the genes nor only by environmental instruction. It involves complicated ongoing interactions between different levels of organization from genes to cells to brain parts to body parts, and all in interaction (or coaction) with specific tasks and with functional activity itself. The meaning of epigenesis has undergone a number of salient changes in meaning since William Harvey (1578-1657) first defined it in the 17th century in his Exercitationes de generatione animalium (1651). The discoverer of the mechanisms of blood circulation, Harvey distinguished between ‘epigenesis’ (differentiation with growth) and metamorphosis or preformationism (differentiation without growth).
See Agentic processes, Dependent differentiation, Development, Differentiation (embryology), Epigenetic landscape, Epigenetics, Evolution, Growth, Homunculus, Innate (1), Plasticity (experiential), Predetermined epigenesis, Preformationism, Probabilistic epigenesis, Self-differentiation