In addition to the distinction between species as a category and speciesas a taxon, the word species is ambiguous in a very different butequally important way, namely the temporal distinction between horizontal andvertical species. Although often found in the relevant literature, thisdistinction has thus far remained vague and undefined. In this paper the use ofthe distinction is explored, an attempt is made to clarify and define it, andthen the relation between the two dimensions and the implications of thatrelation are examined. (...) Using Darwin's analogy of language evolution forspeciesevolution, and by appealing to a major change in the conception of languagebetween 19th- and 20th-century linguistics, it is argued that the horizontaldimension has priority (pragmatic, epistemological, logical, and ontological)over the vertical dimension. This has immense ramifications for the modernspecies problem. Fundamentally, it favors horizontal species concepts oververtical ones. In so doing it places species realism on a much more securefoundation and largely undercuts species pluralism. In addition it raises aserious problem for the increasingly popular family of phylogenetic speciesconcepts, which generally suffer from a dimensionality confusion. However,thereis a recent trend within this family that attempts to restore the priority ofthe horizontal dimension. It is concluded that this trend should be affirmedandthat the species-as-individuals view should be abandoned. (shrink)

What are biological species? Aristotelians and Lockeans agree that they are natural kinds; but, evolutionary theory shows that neither traditional philosophical approach is truly adequate. Recently, Michael Ghiselin and David Hull have argued that species are individuals. This claim is shown to be against the spirit of much modern biology. It is concluded that species are natural kinds of a sort, and that any 'objectivity' they possess comes from their being at the focus of a consilience of inductions.

What are biological species? Aristotelians and Lockeans agree that they are natural kinds; but, evolutionary theory shows that neither traditional philosophical approach is truly adequate. Recently, Michael Ghiselin and David Hull have argued that species are individuals. This claim is shown to be against the spirit of much modern biology. It is concluded that species are natural kinds of a sort, and that any 'objectivity' they possess comes from their being at the focus of a consilience of inductions.

This paper explains the metaphysical implications of the view that species are individuals (SAI). I first clarify SAI in light of the separate distinctions between individuals and classes, particulars and universals, and abstract and concrete things. I then show why the standard arguments given in defense of SAI are not compelling. Nonetheless, the ontological status of species is linked to the traditional "species problem," in that certain species concepts do entail that species are individuals. I develop the idea that species (...) names are rigid designators and show how this provides additional motivation for SAI. (shrink)

_This sweeping discussion of the philosophy of evolutionary biology is based on the revolutionary idea that species are not kinds of organisms but wholes composed of organisms._.