Evolution of multicellular morphogenesis and the morphogenetic impact on evolution

Abstract

In Eukaryotic organisms morphogenesis is linked to peculiar properties of plasmalemma and cytoskeleton. In the Protozoa these properties allow the formation of structures of colonial type derived either from the descent of a single cell or from the confluence of isolated cells. In Plants morphogenesis is linked to the orienting of spindles and divisory plans during mitoses, while in the Metazoa cells reach their position in the embryonic frame by active morphogenetic movements: their number and relative position are controlled by regulating mechanisms.

In Vertebrates also embryonic determination is connected with the position reached by cells on the morphogenetic field. This'position effect’ is the effect of extrinsic and intrinsic factors that reflect the topological pattern genetically acquired from which an harmonic unitary whole emerges.

Embryonic development, following fixed morphogenetic patterns imposes some constraints on evolution, which, however, allow even strongly divergent adaptations to meet different functional needs.

The gaps in our knowledge about the ≪progressive evolution≫ (or ≪great evolution≫) are too great to be bridged at present. Summing up, there is much evidence that biological evolution is a unitary event involving many processes, including natural selection, to which, however, we should not ascribe events that are outside its driving force.

Key words:

• Morphogenesis
• Evolution
• Cell clustering