"The metaphysical doctrine of 'permanent essences' drew empirical support from the success of Aristotle's zoological theory of fixed species, which was its most convincing application to our actual experience of the world. ...[T]he doctrine of fixed organic species simply exemplified, in the special sphere of biology, the permanent character of all 'rationally intelligible' entities. Conversely, Darwin demonstrated that Aristotle's most favored examples failed to support... the metaphysical assumption on which orthodox Greek natural philosophy had been based. Species were not... permanent entities; the earlier 'typological' or 'essentialist' approach to taxonomy inherited from Aristotle misrepresented the long term history of living things. ...However irrelevant the empirical details of Darwin's work may be to general philosophy, the abstract form of his explanatory schema has a much broader significance. So, when Darwin and his successors showed that the whole zoological concepts of 'species' must be reanalysed in populational terms, their demonstration knocked away [a] prop from the traditional metaphysical debate."