 This explicit opposition of two meanings of “species”introduced by Buffon, contrasting concepts previously linked together by a complex relation of thought and world within the Aristotelian and Scholastic discussions, has been seen by some commentators as marking the introduction of a fundamental confusion over the conception of species in subsequent discussions in the biological literature. This is at least one of the underlying causes of the so-called “species problem”. In their historical extension, these issues continue to generate contemporary disputes that oppose conceptions of “species as sets” to those of “species as spatio-temporal individuals” (Dupré 1993; Ereshefsky (ed.) 1992; Ghiselin 1997; Hull 1999; R.A. Richards 2010; Sloan 2013; Stamos 2003; Wheeler &amp; Meier (eds) 2000; Wilkins 2009; R.A. Wilson (ed.) 1999; and the entry on  species  in this encyclopedia).