Title of the session (mandatory): New light on species essentialisms in biology 

 The proponents of the new versions of essentialism claim that they are compatible with evolutionary theory. However, this theory has been built up precisely against ancient forms of essentialism. The aim of the talk is to investigate to what extent the compatibility claim can be defended. My own claim will be that the proponents of new wave essentialism encounter a dilemma:

- either they stick to the compatibilility claim, but then they have to weaken their essentialist position with respect to living species, and transform it into a monist position about the species concept,

- or their essentialism is more than monism about the species concept, but in this case they have to give up the compatibility claim.

In my analysis of the first horn of the dilemma I shall restrict my self to the "biological" and to the "phylogenetic" species concepts, the first one being often refered to by the proponents of essentialism, and the second one being entirely relational.