philosophical taxonomy

Ophelia Benson at Butterflies and Wheels made an ingenious, but we think ultimately misleading, comparison the other day in a post about Gene Sparling’s discovery that the ivory billed woodpecker is not extinct. She finds the story inspiriting – as we do. But the philosophical moral that she draws from it we find, well, unsatisfactory:

“It's kind of a black swan story, kind of a story about falsification, and the difficulty or impossibility of being sure of a negative. It's about the fact we've talked about here more than once: the fact that not having found X does not necessarily mean there is no X to find. It could mean that, but it could just mean you haven't found it. And it can be very very difficult to know which.”

OB adds to this notion of finding and falsification the notion of a scale of far-fetchedness:

“Because Sparling wouldn't let himself think he'd seen what he suspected he'd seen, at first - in fact for quite awhile. Why? Because he didn't want to be ridiculed as a loony, a Big foot finder, an alien abduction believer. And he thought he couldn't have seen what he thought he'd seen. But actually, on consideration, the possibility that it was what he thought it might be except that it couldn't be (because Ivory bills are extinct, he said solemnly, they've been extinct my whole life) is really not nearly as far-fetched as either Big foot or alien abductions. And Big foot, in turn, is not as far-fetched as alien abductions. So there's a scale of far-fetchedness here: 1, 2, 3.”

We think that OB’s comparison between the fabulous search for the black swan, a example enshrined in American philosophy courses, and the search for the ivory billed woodpecker screens philosophically disjoint projects. One is the issue of whether there is such a thing as an x; the other is what kind of a thing x is. Whether a swan can have black coloring is a question of the swan’s properties. It is wrapped up in the larger taxonomic question, what is a swan? Whether the ivory billed woodpecker exists isn’t a question of a property – as Kant showed a long time ago, existence is not a property. It may be that there is an overlap in the method used to research both questions – you may search for black swans or you may search for ivory billed woodpeckers. Or you may even search for yeti. But the level of the scientific issue in which your search gains its meaning will be different.

That philosophers generally ignore taxonomy in preference to theory building is, perhaps, the result of the philosophical obsession with physics as the central natural science, and the search, in physics, for fundamental forces. But taxonomy offers its own philosophical dilemmas. Which brings us to Marc Ereshefsky and Mohan Matthen’s Taxonomy, Polymorphism, and History: An Introduction to Population Structure Theory in this Winter’s Philosophy of Science.

Ereshefsky and Matthen argue against a common taxonomic theory that is built into the various simple problems that have been canonized among philosophers (such as OB’s black swans – or sometimes ravens): the “homeostatic property cluster.” This theory incorporates our naïve way of distinguishing kinds by external properties, and brings it up to date by recognizing that there is a system in which these properties function – the living system, governed by natural selection. “Proponents of this view … hold that while there is no set of properties that all members of a species must share, there is a set of properties that tend to be coinstantiated among the members of a species. These properties …are maintained by “homeostatic mechanisms.” EM argue against this view, which they associate strongly with Richard Boyd, and for what they call Population Structure Theory.’

“What is needed, we suggest, is to move away from the focus on the properties individuals share and to take greater notice of populations and other more inclusive entities. These entities are causal actors in the evolutionary process, and they are so in virtue of their phenotype distributions and their population structures.”

To rephrase the black swan example in PST terms, here’s the question for philosophers: is it possible to find a swan with a chimpanzee genome? Here we are reaching down from the way in which we describe outward properties to properties of descent. That there is a lack of work on this kind of thing in philosophy points to the philosophic preference for logic over structure. And that has had the effect of making it seem like questions of structure are secondary. But of course they aren’t.

For instance: when we search for whether swans are defined by their coloration – for black swans, for instance – we think we are being guided by a correlation between what swans look like and what swans are. And because even duckling swans have certain recognizable traits that are similar to adult swans, we can still look among swan ducklings for the ugly one that grows up to be a different colored swan. But what about butterflies? To speak of monarch butterflies in a scientific sense, we have to incorporate both the caterpillar and the mature butterfly. They look so different that searching the appearances, here, has to be conducted according to much other lines than simply, monarch butterflies all have orange wings with black spots. And what about the differences brought in by species that have very distinct appearance differences between males and females? Hence, the polymorphism in EM’s title. We know that there are species that look so different during their life cycles that they have been erroneously classified as separate species. We know that certain seeming species – lichens, for instance – have turned out to be several species living symbiotically.

All of these things push us to ask questions about “looking for x” and the idea that falsification plays a central and defining role in science. Which we will take up again tomorrow.