Among biological kinds, the most important are species. But species, however defined, have vague boundaries, both synchronically owing to hybridization and ongoing speciation, and diachronically owing to genetic drift and genealogical continuity despite speciation. It is argued that the solution to the problems of species and their vague boundaries is to adopt a thoroughgoing nominalism in regard to all biological taxa, from species to domains. The base entities are individual organisms: populations of these compose species and higher taxa. This accommodates all the important biological facts while avoiding the legacy problems of pre-evolutionary typological taxonomy, which saw species and other taxa as prior to their members. Species are however not individuals: they are spatiotemporally bounded collections, which are plural particulars.
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I proposed this in a letter to Ernst Mayr and he did agree that the idea of a highly scattered individual was strained.
I have been advocating concrete pluralities since Simons (1980).
The type of a genus or higher taxon is a type of one of the species subordinate to it.
In unpublished work with Yu Lin, we propose a nominalist account of DNA sequences, using mereology and a nominalistic account of sequences (strings).
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A class the members of which are all the taxa placed at a given level in a hierarchic classification (Simpson 1961: 19)
Offspring of a male lion and a tigress
A group of real organisms recognized as a formal unit at any level in a hierarchic classificationFootnote 5
Offpring of a male tiger and a lioness