John Locke on species

Abstract

The philosopher and natural scientist John Locke argued in his Essay concerning human understanding (1690) that there are no natural clear limits to species even of living things, only man-made arbitrary limits. He was convinced that the properties of so distinctive a substance as gold were at least in part variable; that ice and water were rightly separate species to those who had different names for them; that all sorts of living things produce on occasion monsters which are new species; and that a cat and a rat can miscegenate, producing something that is neither. For Locke and nearly all his contemporaries these difficulties were found in defining both inorganic and organic species, all natural (and indeed artificial) species being of the same sort. For Locke, the essences (inmost constitutions) of natural things were unknowable except by special revelation; and their taxonomy was necessarily of unanalysed entities, called in this paper a phenotaxonomy; whereas in such entities as geometrical figures, the definition did express the essence, giving the basis for a lysotaxonomy of analysed entities. The difficulties of reference in a phenotaxonomy pushed Locke towards the modern type-system. Give the accepted factual knowledge of the time, in assessing which Locke was not very critical, the wonder is not that he rejected the criterion of common parentage for members of the same living species, but that the naturalist John Ray accepted it.