THE EFFECT OF ESSENTIALISM ON TAXONOMY—TWO THOUSAND YEARS OF STASIS (I) *

A CONVENIENT year to designate as the beginning of the scientific revolution is 1543. In that year Nicholas Copernicus published De Revolutionibus Orbium Coelestium and Andreas Vesalius published De Humani Corporis Fabrica. In a little more than a hundred years classical physics reached its fruition in Newton's Principia. At first biology promised a similar development with the work of Leewenhoek, Schwammerdam, and Malpighi, but no theoretical achievements even vaguely comparable to those in physics were forthcoming. It wasn't until the nineteenth century with the work of Darwin and Lamarck on evolution, of Mendel on genetics, of Pasteur on micro-organisms, and of Schleiden and others on cell theory that biology came of age. In taxonomy the scientific revolution has been even slower in making itself felt. Although John Ray and Carolus Linnaeus made some advances in the methodology of taxonomy and in organising their taxa, they made no significant contributions to taxonomic theory as devised by Aristotle. As biology lagged behind physics in divesting itself of scholastic influence, taxonomy lagged far behind the other biological sciences. In fact, contrary to popular opinion, the process is still far from complete. And taxonomy only now is reaching a stage of maturity comparable to that of physics 300 years ago or to that of other biological sciences of fifty or a hundred years ago. Why is this? Karl R. Popper's answer is that ' the development of thought since Aristotle could, I think, be summed up by saying that every discipline as long as it used the Aristotelian method of definition has remained arrested in a state of empty verbiage and barren scholasticism, and that the degree to which the various sciences have been able to make any progress depended on the degree to which they have been able to get