Olivier Rieppel

The German tradition of considering species, and higher taxonomic entities, as individuals begins with the temporalization of natural history, thus pre-dating Darwin’s ‘Origin’ of 1859. In the tradition of German Naturphilosophie as developed by Friedrich Schelling, species came to be seen as parts of a complex whole that encompasses all (living) nature. Species were comprehended as dynamic entities that earn individuality by virtue of their irreversible passage through time. Species individuality was conceived in terms of species taxa forming a spatiotemporally located relational system (complex whole), a conception of species that was easily assimilated to an evolutionary world view. However, the dynamics of an evolutionary process driven by variation and natural selection created a tension between continuity in nature as opposed to the discreteness and relative stasis of species. As a consequence, some authors such as Ernst Haeckel and Karl August Möbius denied the reality of species, while others explicitly linked the reality and individuality of species to their temporal duration. The mature conception of species as individuals, as formulated by Ludwig von Bertalanffy and adopted by Willi Hennig, is one of an historically conditioned, spatiotemporally located, causally integrated, dynamic yet transiently homeostatically stabilized relational system.

The architects of the modern synthesis banned essentialism from evolutionary theory. This rejection of essentialism was motivated by Darwin’s theory of natural selection, and the continuity of evolutionary transformation. Contemporary evolutionary biology witnesses a renaissance of essentialism in three contexts: “origin essentialism” with respect to species and supraspecific taxa, the bar coding of species on the basis of discontinuities of DNA variation between populations, and the search for laws of evolutionary developmental biology. Such “new essentialism” in contemporary biology must be of a new kind that accommodates relational (extrinsic) properties as historical essences and cluster concepts of natural kinds.