Meeting 8: A Different Kind of Natural Kind (3/4)

Readings:

• Boyd, “Homeostasis, Species, and Higher Taxa” [PDF]
• Slater, “Why the Long Face? The Stable Property Cluster Account of Natural Kinds” [PDF]

As we've seen, the thesis the biological taxa have essential properties (like those supposedly possessed by physical and chemical kinds), looks rather implausible. Since the concept of a natural kind is usually bound up with notion of an essence — a defining characteristic of the kind —, the fall of essentialism has meant for many a denial that species (and other biological taxa) are natural kinds. Indeed, this is a major motivation behind the move to the species-as-individuals thesis. If species are real and not natural kinds, then they must be individuals! I believe that this argument possesses a false premise (that species are not natural kinds) and is fallacious (in particular, it seems a false dilemma to think that species must be either natural kinds or individuals. Perhaps species might fit in another ontological category or perhaps, as I suggested in my "Contentious Metaphysics of Species" paper, species might not be anything and we should instead focus on how to reconstruct talk of species in an ontological non-committal way (e.g. using plural quantification).

The thesis that natural kinds must possess essences, though natural and popular, does not seem to be part of the concept of a natural kind. Their inferential and explanatory role is, to my mind, more central. We’ll focus on a strand of anti-essentialism committed to this stance. Richard Boyd (a philosopher at Cornell) is perhaps the best known defender of anti-essentialism about natural kinds — though I should immediately point out that it is somewhat controversial whether his view should be reckoned as "anti-essentialist" (this is something I'll want to talk about). He defends what he calls a “homeostatic property cluster” (HPC) account of natural kinds on which rather than an essence maintaining the correlation among a bunch of properties we associate with a given kind, the properties, in a way, correlate themselves. No one property among this “cluster” of properties need be regarded as the essence of that kind — they all are. Nor must we view all of the properties as necessarily possessed by members of the HPC kind. The relevant homeostasis may be imperfect, after all.

I find this picture very appealing. But I’m not certain what counts as a homeostatic mechanism and what is meant by certain phrases Boyd uses to cash out this notion: “the causal structure of the world” and so on. This quibble can be answered, I suppose. One answer I can imagine is: “Oh, come on! You know well enough what I mean by ‘the causal structure of the world’! It’s the whole causal economy: the way things work, how everything fits together, what science studies.” But even supposing something like this helped (and I don’t see that it does), a bigger problem for the HPC view is that the kind of homeostasis that Boyd assumes is present is often apparently lacking: say, for higher taxa, species undergoing disruptive selection, or taxa (at the species rank and otherwise) whose coherence is maintained by “phylogenetic inertia”. It seems to me that all we are really committed to with the reality of species is their broad explanatory utility and this can be secured simply by the stability that the relevant cluster of properties features. I defend this thesis in more detail in my “Why the Long Face?” using examples other than species. The paper is a bit on the long side (sorry — this is actually the SHORT version, believe it or not), so you can skim section 2 if pressed for time (you've already heard my views on many of these issues).

Study Questions

• Briefly describe what an HPC natural kind is. How does it help address the problems facing typological thinking?
• What is Boyd’s accommodation thesis?
• How does the essentialism espoused by Boyd differ from a more “traditional” essentialism about natural kinds?
• What is Boyd’s stance on species pluralism?
• How do explanatory and programmatic definitions differ?
• Does Boyd think that there is an important distinction between species and higher taxa (such as genera)?
• Peacocke draws a distinction between narrow- and wide-scope explanations. Describe it and explain how it is relevant to the discussion of the HPC account.
• Describe a criticism of mine of the HPC view. Do you think Boyd could offer a compelling response?
• What specific problem is posed by disruptive selection?
• What is metastability and how might it be relevant to the discussion of HPC kinds?
• Why is stability important for a potential understanding of natural kinds? What role might it play in such understandings?
• How does the SPC account differ from the HPC account?