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The Origins of Species Concepts

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The Origins of Species Concepts The origins of species concepts History, characters, modes, and synapomorphies John Simpson Wilkins Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy November, 2003 The Origins of Species Concepts Abstract The longstanding species problem in biology has a history that suggests a solution, and that history is not the received history found in many texts written by biologists or philosophers. The notion of species as the division into subordinate groups of any generic predicate was the staple of logic from Aristotle through the middle ages until quite recently. However, the biological species concept during the same period was at first subtly and then overtly different. Unlike the logic sense, which relied on definitions of the essence of both genus and species, biological species from the time of Epicurus were consistently considered to involve a reproductive element: in short, living species relied not on essential definitions, but on the generative cause, which might not be definable. I term this the generative conception of species: species were the generation by reproduction of form. This undercuts the claim that species before Darwin were essentialist, and divorces the notion of a type from that of essence. In fact, as late as the end of the nineteenth century, logicians explicitly treated biological “species” as a homonym only of logical essentialist species, and permitted considerable deviation from the type or form. At every point, species in logic were thought to be a subset, in effect, of some more general notion. I sketch a history of both philosophical and biological traditions of the species concept, before turning to the current conceptions. These are reconsidered in the light of this history, and in particular Mayr’s changing views are shown to be somewhat Whiggish, historiographically. Of the many touted biological species concepts, only one of which (Mayr’s) is called the Biological Species Concept, none appears to capture all the relevant facts, intuitions, and operational requirements of biology. Cladistic conceptions, however, have much in common with the older philosophical literature, in that the natural group of cladism is the clade, or monophyletic group. After considering the Individuality Thesis, and the metaphysics of species, we see that species are the most particular terminal taxa in a clade, and that they are “defined” in terms of the particular synapomorphies, or evolved characters, that are causally responsible for keeping the lineages that organisms form distinct from one another. In this way, we can remain within the generative conception of species that has been in play for over two millennia, and yet avoid the pitfalls of prior attempts to find a universal conception of species. Page ii The Origins of Species Concepts Declaration This is to certify that (i) the thesis comprises only my original work towards the PhD except where indicated in the Preface, (ii) due acknowledgement has been made in the text to all other material used, (iii) the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliographies and appendices. The Origins of Species Concepts [Complex ideas] have their union and combination only from the understanding which unites them under one name: but, uniting them without any rule or pattern, it cannot be but that the signification of the name that stands for such voluntary collections should be often various in the minds of different men, who have scarce any standing rule to regulate themselves and their notions by, in such arbitrary ideas. John Locke, Essay on Human Understanding III ix 8 Dedication To my wife Paula and children Alice and John Nathaniel, who endure my obsessions with grace and resignation; and to David Hull and the late David Rindos, who both encouraged me. Page iv The Origins of Species Concepts Contents Abstract ....................................................................................................................................ii Declaration ...................................................................................................................................iii Dedication ...................................................................................................................................iv Figures ..................................................................................................................................vii Tables ..................................................................................................................................vii Preface .................................................................................................................................viii Chapter 1. Philosophy and the species problem................................................................... 1 1.1. Ideal Species Concept .................................................................................................................................... 1 1.2. Natural and artificial...................................................................................................................................... 3 1.3. Species realism ................................................................................................................................................ 6 1.4. Three species problems ................................................................................................................................. 8 1.4.1. Grouping problem......................................................................................................................... 9 1.4.2. The ranking problem .................................................................................................................... 9 1.4.3. The commensurability problem...............................................................................................10 Chapter 2. A philosophical history of the species concept...............................................12 2.1. Received History...........................................................................................................................................12 2.2. Universal taxonomy.....................................................................................................................................20 2.2.1. Plato................................................................................................................................................21 2.2.2. Aristotle .........................................................................................................................................23 2.2.3. Epicureanism................................................................................................................................28 2.2.4. The Hermetic tradition...............................................................................................................31 2.2.5. The neo-Platonists.......................................................................................................................31 2.3. Post-medieval period...................................................................................................................................36 2.3.1. Nicholas of Cusa ..........................................................................................................................36 2.3.2. Marsilio Ficino .............................................................................................................................38 2.4. Great Chain of Being ...................................................................................................................................39 2.5. Universal Language Project........................................................................................................................42 2.6. Death of essentialism ...................................................................................................................................45 2.6.1. Locke and Leibniz –real and nominal essence.......................................................................45 2.6.2. Immanuel Kant and the continuity of species.......................................................................48 2.6.3. Nineteenth century logic............................................................................................................51 2.7. Summary and conclusions..........................................................................................................................55 Chapter 3. Biological Taxonomy ...........................................................................................57 3.1. Beginnings......................................................................................................................................................57 3.1.1. Cesalpino and Bauhin – the beginnings .................................................................................57 3.1.2. John Ray – propagation from seed...........................................................................................59 3.1.3. Carl Linnaeus – species as the Creator made them ..............................................................61 3.1.4. Buffon – degeneration, mules, and individuals.....................................................................65 3.1.5. Charles Bonnet and the ideal morphologists.........................................................................69 3.1.6. Essentialism and natural systems .............................................................................................71
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