It is commonly believed that the debate on the nature of living species and their possible evolution has no real history prior to the 18th century. The roots of this assumption lie in the belief that the entire previous tradition had been dominated by the combination of the Aristotelian doctrine of the eternity of species (fixism) and Jewish, Christian and Islamic creationism. The core hypothesis of SPECIES is that, on the contrary, the Middle Ages produced a significant and sophisticated series of reflections on the constancy and fluidity of species, and that the originality of these doctrines can be traced to the use of arguments based on divine omnipotence. The ambition of SPECIES is to rewrite the history of the concept of species. To this end, it will develop through four specific questions, which correspond to the four fundamental objectives [O] of the project: 1. [ORIGO] Are species eternal or do they have a temporal beginning? O1: Show that pre-evolutionary theories are by no means a monolithic and undifferentiated whole. 2. [ORDO] Do species represent an unchanging essential order or can they be subject to variation? O2: Show that hypotheses relating in various ways to the variability or new generation of species arose and were discussed long before the 18th and 19th centuries. 3. [PRAEDICATIO] What is the relationship between species as natural kinds and species as logical predicables? O3: Clarify the relationship between logical and natural classifications in the pre-modern period, allowing a precise disambiguation of the different meanings of ‘species’. 4. [DESCENSUS] Are species hierarchically ordered among themselves? And do they allow for any internal subdivision? O4: Offer a first precise reconstruction of the genesis of a number of (still) burning issues, such as those related to intraspecific racism, speciesism, and the balance between individual and specific interests (a topic of increasing interest in the field of intergenerational ethics).