Synchronic species aren’t diachronic species: why 3D/4D metaphysical equivalence fails for the case of biological species

The debate on the temporal persistence of entities is characterized by the opposition of two principal positions, three-dimensionalism (endurantism) and four-dimensionalism (perdurantism). Some authors have suggested that this opposition is misguided, because three-dimensionalism and four-dimensionalism are metaphysically equivalent accounts of persistence (3D/4D metaphysical equivalence). Recently, the case of biological species has been used as an example to argue that 3D/4D metaphysical equivalence does not hold in all cases, because different species concepts refer to different kinds of entities, some of which are best conceived of as three-dimensional entities while others are best seen as four-dimensional entities. This argument has not settled the question of 3D/4D metaphysical equivalence, however. The present paper revisits the debate by addressing new arguments that have been introduced recently and examining four assumptions on which these arguments rest. It is argued that these assumptions are problematic and shows why the thesis of 3D/4D metaphysical equivalence should still be rejected.