Biological Species Are Natural Kinds

This paper argues that typical biological species are natural kinds, on a familiar realist understanding of natural kinds-classes of individuals across which certain properties cluster together, in virtue of the causal workings of the world. But the clustering is far from exceptionless. Virtually no properties, or property-combinations, characterize every last member of a typical species-unless they can also appear outside the species. This motivates some to hold that what ties together the members of a species is the ability to interbreed, others that it is common descent. Yet others hold that species are scattered individuals, of which organisms are parts rather than members. But not one of these views absolves us of the need to posit a typical phenotypic profile. Vagueness is here to stay. Some seek to explain the vagueness by saying species are united by "homeostatic property clusters"; but this view collapses into the more familiar realist picture.