Meeting 5: Biological Kinds (2/11)

Required Readings:

• Ridley, “Species Concepts and Intraspecific Variation” [Chapter 13 of Evolution; PDF] **
• Slater, "Natural Kinds" [PDF] --- forthcoming! **
• Mayr, “Typological versus Population Thinking” [CIEB §16]
• Sober, “Evolution, Population Thinking, and Essentialism” [CIEB §17] *
• Dupré, "Natural Kinds and Biological Taxa" [PDF]

This week, we’ll enter into a tangle of issues that will detain us for the next four or so meetings. Our initial focus will be on how the fact of evolution by natural selection impinges on classification. We'll start by talking about the notion of a natural kind. Sorry my survey article is not yet done! I should have a draft ready to share by the weekend. Because it's not ready, I list it as optional. I'll add another post when it's ready for prime-time. Here's the basic idea, though: some scientific categories — electron, water, tiger, &c. — appear to be more "natural" than others in a sense that deserves careful attention. How are we to make sense of this?

The traditional way is by construing some categories (which we call "natural kinds") to be characterized by essential properties — qualities which make things of a particular kind the things of that kind. The late, great biologist (one of the chief architects of the so-called “modern synthesis” of evolutionary biology) Ernst Mayr takes Plato to task for attempting to apply an eidos (something like an abstract type; see CIEB, p. 326) to species. While he’s correct that the notion probably originated with Plato and his theory of forms, it received a much more sophisticated and unmysterious expression with Aristotle. He believed that there was some property (or group of properties) that qualified an organism as the kind of thing it is. Ditto for other examples. Water is a favorite example of modern essentialists like Kripke and Putnam. According to them, the essence of water is having that molecular structure (the one denoted by ‘H2O’); something is water just in case it is composed of H2O and even if that something still looked like and behaved like water. (So goes the thought. My own feeling is that this is much less clear than might at first appear.) However that may be, it was widely thought that species have essences and that this is what makes them real.

But essentialism underpins what Mayr calls "typological thinking". And essentialism may be at the root of many of typology’s supposed ills. Against Aristotle and Plato, I agree with Mayr that we should construe variation as the norm in the biological realm. But there are difficult interpretive questions about what population thinking means for Mayr and how it ought to influence how we conduct and conceive of biology. John Dupré takes on essentialism via Kripke and Putnam's more sophisticated version. He is much exercised by the mismatch between scientific taxonomies and ordinary language classifications.

Study Questions

• What is the basic difference between typological and population thinking?
• Mayr argues against the thought that evolutionary gradualism and typological thinking are compatible. Explicate and evaluate this argument.
• What role does Putnam's "Twin Earth" thought experiment play?
• How does Dupré respond to the Twin Earth thought experiment? Are you sympathetic or has Dupré exaggerated the problems?
• What exactly is the worry about the lilies? Is it serious?
• Do you think that taxonomic realism is more or less plausible at higher levels of classification than species? What is Dupré's view on this question? What about Mayr?
• What reasons are there to be pessimistic that the "privileged sameness relations" Putnam seems to need for his theory exist at the level of species?