This chapter explains Darwinism by providing evidence of its status of historical a-priori; a status that post-constructionist social theory does not bring into question but assumes in the form of ontology of difference, enacted by the machine of efficient causality. It focuses on major problems and circularities of evolutionary theory, which indicate its metaphysical underpinnings and bring into question the ontological value of its claims. The chapter discusses the most interesting alternative to the Darwinian a-priori: Heidegger's anti-metaphysical account of the human being and its relationship with the world. To define Darwinism as the historical a-priori of the present may sound as an overstatement. However, for a start, Darwinism offers an account of life that fits perfectly the physicalist option that has been gaining relevance since Descartes division between res cogitans and res extensa, and of which the ontological turn offers an accomplished version. The relationship between brain and mind has always puzzled Darwinian scholarship.