ABSTRACT
All evolution of multicellular animals is the brilliant result of altering developmental programmes. In the evolution of gastrulation and its conservation in different animals, there are at least two separate processes that need to be considered- the setting-up of the main body plan and the morphogenetic movements. It is possible that the embryo is evolutionarily privileged; that is, the main selective pressure is for reliable development. If morphological variants that do not affect the later stages in development are not subject to selection, then they will persist and can provide the basis for the evolution of novelty. Gastrulation can be thought of as one of the most important processes in early development. Its evolution probably did not require any significant mechanisms absent from the eukaryotic cell. Gastrulation may represent a very primitive metazoan whose development has been elaborated and extended in evolution.
