Atomism, epigenesis, preformation and pre-existence: a clarification of terms and consequences

The meaning of the terms atomism, epigenesis, preformation and pre-existence is clarified by a historical analysis. Today, two alternative models of organismic change are opposed to each other. Atomism views the organism as being composed of traits or atoms: it implies the possibility of gradualistic change and a nominalistic species concept, while an increase in complexity is identified as an addition of new parts. Epigenesis, in contrast, implies the possibility of saltational change and an essentialistic species concept, while an increase in complexity is considered to result from an enhanced compartmentalization and differentiation of the originally homogeneous primordium. Schwabe & Warr's (1984) 'genetic potential hypothesis' qualifies as pre-existence at the genotypic level.