Originally introduced into evolutionary biology by Gavin de Beer (1899-1972) to account for evolutionary change in the onset or timing of development. Applied to development, it portrays it as a mixture of different timings in the appearance of structures and functions, with some being accelerated and others relatively retarded. Slower developing structures and functions act as constraints on the process of developmental change and which are ‘lifted’ once they mature, resulting in the emergence of new abilities. Systemogenesis, as devised by Pyotr Anokhin (1898-1974), is an attempt to account for the adaptive significance of heterochronicity in development, and especially for adaptation to extrauterine environment in the newborn. He distinguished between two forms of heterchrony: intra-systemic heterchrony (the unequal onset of initial organization and the different maturation of the components of the functional system) and inter-systemic heterochrony (the initial organization and moment of development of those structural components that constitute the basis for different functional systems).
See Constraint, Developmental emergence, Emergence, Organogenesis, Systemogenesis