Abstract

Abstract. Animal evolution is seen today through the dilemma of two reigning views. The first sees animal evolution as a shallow sequence of contingent accidents and catastrophic extinctions. The second ,accepting a progressive trend in this evolution, sees a hidden vitalistic or deistic force at work. I propose a third way which accepts progressivism , but considers it to be a historical consequence of directional dissipative thermodynamic processes which are acting on the globe. The animals have a crucial role in stimulating the gradual expansion of the biosphere and the increasingly efficient recycling within it. The different animal phyla, irreversibly marked by their morpho-physiological signatures are the selective and selected players in this process. The terrestrial environment, once colonised, provides for maximum biomass and highest animal efficiency and complexity. The thermoregulating vertebrates and among them the human species selected out as the recent culmination of this evolution.