Ontogenesis and Morphological Diversification

SYNOPSIS. The role of development in constraining the directionality and patterns of morphological evolution is examined. The nature of morphological variation and appearance of morphological novelties is determined by the epigenetic properties of the organism. Consideration of these properties has profound implications for current theories of morphological evolution. Developmental constraints impose severe limitations on the gradualistic action of directional selection. Evolutionis viewed as the result of differential survival of morphological novelties. However, the production of morphological novelties by developmental programs is not random. This non-randomness in morphologically expressed genetic mutations—an epigenetic property—can result in phyletic trends, parallelisms and convergences.