ABSTRACT
Many scientists and philosophers have said something like “species are the units of evolution” or “the units of biodiversity”; it is even the title of some well-known books on the subject (Ereshefsky 1992; Claridge et al. 1997). What does this even mean? In this chapter I argue that species are real, phenomenal objects rather than objects of any biological theory, let alone of evolutionary theory. Species is a term which everybody thinks they understand, but which nobody agrees upon, to denote the “basic units” of groups of biological organisms. Philosophically, there have been three stances taken in the past fifty years: the species essentialist view that all organisms of a species must share some (usually genetic) properties (Devitt 2008); the individualist view that species are historical objects without essences (Hull 1976, 1978); and the homeostatic view that species are coherently maintained objects due to some causal processes (Boyd 2010).
