I. Divisions into Species

Animals are living beings defined among other living beings and by a specific animal: the human animal. Animality is defined through a division of living things into kingdoms, themselves divided into branches, classes, orders, families, genera, and species. Species are the fundamental classes of the division of living things. The divisions into species make animal species events rather than objects.

In the history of Western knowledge, species were once a principle of dividing several things into objects, which were dependent upon the living object's ancestral relations and resemblances. Georges Cuvier's fixist conception of species 'includes the individuals which descend from one another, or from common parents, and those which resemble them as strongly as they resemble one another.'Augustin Pyramus de Candolle soon after recast Cuvier's fixist classificatory system. But the introduction of an evolutionary concept of living things, in which form passes through genetic information and its transmission through self-levels, affected the definition of species considerably. Ernst Mayr's and Theodosius Dobzhansky's important work contributed to the establishment of the twentieth-century neo-Darwinian synthesis. In 1942, Mayr famously defined a concept of biological species that broke with idealism and 'typological thought': 'species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups'.Mayr's use of the term 'potentially' reintroduces into the definition something it aimed to avoid (an abstraction). The import of Mayr's work lies in the following: a species is a division of living things that does not account for the existence of extraordinary types, dear to the taxonomists and amateurs of cabinets of curiosities – thus,

no criteria of resemblance, morphology, or external form permits us to define a single type or idea of species among the diversity of individuals.