Biological species are spatio-temporally localized entities. This fact led to the concept of species as individuals , , and, at the same time, to the refutation of essentialism in evolutionary biology and taxonomy. On the other hand, molecular biology is compatible with essentialisms of chemistry and physics. The new concept of "historical essences", which is presented in this paper, tries to reconcile antiessentialism of evolutionary biology with essentialism of molecular biology. Historical essences are those parts of genetic information which determine characters relevant for the identification of a taxon. Since membership in a particular taxon is defined by the sharing of the most recent common ancestor, historical essences correspond to the genetic information (organismal blueprints) responsible for the creation of such common ancestor. Historical essences, which are spatiotemporally localized, generate a particular arrangement of spatiotemporally unrestricted processes which lead to the creation, maintenance and reproduction of organisms. These arrangements are results of fortuitous confluence of biological and extrabiological circumstances (evolutionary process). In historical essences such a sequence of historical contingencies is "conserved", which allows molecular taxonomy to reconstruct the phylogenetic relationships. The concept of historical essences can be seen as a post-Darwinian modification of the original Aristotleś term of essence - "to-ti-en-einai".