Drakes, seadevils, and similarity fetishism

Homeostatic property clusters (HPCs) are offered as a way of understanding natural kinds, especially biological species. I review the HPC approach and then discuss an objection by Ereshefsky and Matthen, to the effect that an HPC qua cluster seems ill-fitted as a description of a polymorphic species. The standard response by champions of the HPC approach is to say that all members of a polymorphic species have things in common, namely dispositions or conditional properties. I argue that this response fails. Instances of an HPC kind need not all be similar in their exhibited properties. Instead, HPCs should instead be understood as unified by the underlying causal mechanism that maintains them. The causal mechanism can both produce and explain some systematic differences between a kind’s members. An HPC kind is best understood not as a single cluster of properties maintained in stasis by causal forces, but as a complex of related property clusters kept in relation by an underlying causal process. This approach requires recognizing that taxonomic systems serve both explanatory and inductive purposes. 1 HPCs in a nutshell Samuels and Ferreira write that “philosophers of science have, in recent years, reached a consensus — or as close to consensus as philosophers ever get — according to which natural kinds are Homeostatic Property Clusters” [18, p. 222]. ∗This paper is part of a larger work on natural kinds, written while I was a visiting fellow at the Center for Philosophy of Science at the University of Pittsburgh. My productivity while there was due in no small part to vigorous interaction with many clever and helpful people; among these were Pierluigi Barrotta, Jonathan Birch (who convinced me to think about anglerfish), Kareem Khalifa, Bert Leuridan, Joseph McCaffrey (who pointed me toward bone worms), Sandy Mitchell, John Norton, Richard Samuels, Samuel Schindler, Peter Vickers, Ioannis Votsis, and James Woodward. An earlier version of this paper was presented at Metaphysics & the Philosophy of Science (Toronto, Ontario; May 2011) and improved in light of feedback at the conference, especially from Juha Saatsi, Matthew Slater, Joel Velasco, and Rob Wilson. Thanks also to Marc Ereshefsky, the editor of this journal, and referees for comments on earlier drafts.