Term: cenogenesis: introduction during embryonic development of characters or structure not present in the earlier evolutionary history of the strain or species (such as the addition of the placenta in mammalian evolution)
Broader: growth: (biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level | Unrelated: current: a steady flow of a fluid (usually from natural causes)