Termination of Organogenesis as Intrinsic Constraint on Animal Development and Evolution: A Theory

In this article, it is pointed out with integrative analysis that organogenesis manifests limitation in time and possession of termination, while infinite cell proliferation called as cancer and tumor is lethal. Besides, it is reversely demonstrated from a few notable constant outgrowing skin derivatives that termination is required for organogenesis inside the animal. Accordingly, it is suggested that the requirement for organogenetic termination would be the new intrinsic constraint for animal development and heredity. In further, it is suggested from comparative analysis that this new intrinsic constraint would not influence the temporal and spatial reorganization of morphogenesis, but place restrictions on alteration of organogenetic mechanisms themselves. Especially, it is pointed out that addition of new induction mechanism or elimination of termination mechanism would usually cause endless organogenesis and lethality, subjecting to restriction by the intrinsic constraint, while addition of new termination mechanism or elimination of induction mechanism not be affected by the intrinsic constraint, occurring more frequently in evolution. In accordance, it is identified this intrinsic constraint as the pertaining cause for frequent occurrence of developmental parallelism and terminal addition in animal evolution as recapitulation. In this article, it is also provided with some animal models to demonstrate the evolution of organogenetic termination as key developmental control, such as the hair and nail in humans, the sexual dimorphism in mammary glands, the epidermal scale in reptiles, the tail metamorphosis in amphibians, and the variation in limb digits in vertebrates.