Evolution and classification : the reformation of cladism / Mark Ridley.

  • Ridley, Mark.
Date:
[1986], ©1986
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Evolution and classification : the reformation of cladism / Mark Ridley. Source: Wellcome Collection.

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    1 The argument As the theory of evolution, in the last two decades, has enjoyed a great infusion of fundamental and far-reaching ideas, the philo¬ sophy of classification has not escaped re-examination. It is now an opportune moment to look again at the proper relation of classification and evolution, not least because (if I am correct) the most influential new idea in this area is utterly mistaken. Because the various schools of classification stand in different relations to the theory of evolution, we can consider the question by a discussion of the schools and their rival merits. In order to discuss the schools, we must first be introduced to them; and if the discussion is to be of any interest it must come to a positive conclusion, for if it did not, we should merely have replaced the problem of ignorance by one of confusion. In this work, therefore, I have three main aims, which I shall attempt roughly in order: to introduce the various schools of classification; to examine their rival merits; and (in judging them) to discover the proper relation of evolution and classification. It is an introduction to, and a work of, taxonomic controversy. That there should be any controversy at all might, to begin with, seem strange. The principles of classification, considered superficially, might seem too straightforward to be controversial: you simply have to define groups by taxonomic characters (where 'we understand by taxonomic character any attribute of an organism (or better, of any group of organisms) by which it may differ from other organisms', Mayr 1942, p. 20). And if taxonomists are observed superficially, that is what they appear to do. They order living forms by arranging them in groups according to shared characters. More and more inclusive groups are defined by more and more generally shared characters, to result in the customary hierarchy of species contained in genera, families, orders, classes, phyla. Any form of life is classified by its characters: horses, for instance, are chordates because at some stage in their lives they possess a hollow dorsal nerve chord, segmented muscles, and a notochord; mammals because they are homeothermic 1