The Idea of a Natural Kind
The concept of a natural kind has a long and contentious pedigree, but the basic idea can be illustrated by thinking about some contrasts. The first contrast is between individual things and kinds of things. Here’s a panda; there’s another panda. What do they have in common? They’re both of the same kind. We thus organize a lot of our thought and talk by dividing things up into different conceptual categories like this. The sciences in particular are rife with these efforts to classify and understand nature. This leads to the second contrast. Consider the classic films “Psycho” and “The Silence of the Lambs”; like our pandas, these individuals can be placed in a few common categories: they are both “thrillers”, they are both R-Rated movies, and so on. But there appears to be an important difference between the kinds thrillers and pandas. Only the latter is a natural kind — a category with some objective existence — the former appears to be a byproduct of our more or less arbitrary way of dividing up the word.

While these may seem like clear cases, contrast between natural or “real” kinds and artificial kinds can be difficult to draw and characterize (indeed, it is matter of current dispute whether biological species are natural kinds). Are there natural kinds of people? Do races, for instance, represent genuine divisions in the world or are they more like categories of films: projections onto the world by us? Or perhaps there are some other natural kinds of people representing certain ensembles of traits. Such questions would appear to be of interest to eugenicists interested in manipulating the “sorts of people” ,and whether certain traits are natural or artificial.

What Kinds are “Natural”?
Philosophical discussion of natural kinds can be traced back to Plato and his bloody metaphor of carving nature at its joints. Consider the task of a butcher dividing an animal into different cuts of meat for sale. An inexperienced butcher might make the mistake of cutting through bone, dulling his knife in the process — better to carve at the natural discontinuities. Applying the analogy to the sciences, we might say that the categories of some past theories failed to find the divisions corresponding to the natural kinds in the world. Unlike well-established categories like gold or electron from the mature sciences, past theories posited categories — like phlogiston or caloric — that “cut across the bone”, dividing the world in unnatural and ultimately unproductive ways.

One might wonder at this point how we should understand ‘natural’. Should we see natural kinds as only those categories “produced by nature”? After all, this provides us with a tidy understanding of the difference between the categories of pandas and thrillers. Unfortunately, this won’t quite do; for there are artificially-produced kinds — such as the element technetium — that despite needing to be produced in a lab setting seem just as much to be natural kinds as gold or hydrogen do. For this reason, some authors — John Stuart Mill chief among them — prefer ‘real kinds’ to ‘natural kinds’. The choice does not matter much, however, so long as ‘natural’ is not taken to imply ‘free from human “contamination”’. After all, some elements are human artifacts, yet this does not seem to disqualify them from serving the sort of roles that natural kinds ordinarily serve in science.

Eugenicist Applications of the Natural Kind Concept
This latter point is especially important in the context of discussions of eugenics — for one way of reading what Galton and later eugenicists were trying to do is manipulate what kinds of people exist. For example, the purported category of criminal, while on its face an artifact of social conventions (we might define a criminal as someone disposed to break socially-enacted laws), might nevertheless be understood as stemming ultimately from their underlying genetic makeup. Ditto categories explored by eugenicists, such as epileptics, paupers, or the feeble-minded. While these categories might have conventional definitions referencing certain social institutions that just happen to exist, eugenicists might propose that the traits that make some a pauper, say, inevitably stem from that person’s heritage.

However the question remains: if not isolation from human influence, what distinguishes natural kinds from subjective, conventional kinds? What is so useful about attuning our categories to natural kinds? There are a number of potential answers to these questions. Many, however, focus on the role that natural kinds seem to play in our making inferences and providing explanations. The dispute typically involves how this epistemic utility is achieved. Mill’s account involved the claim that the members of a real kind agreed in an inexhaustible number of ways. While not all have gone in for this stringent requirement, Mill’s belief that members of a kind should be alike in many respects remains popular.

One influential idea on how this should work was a reworking of an idea of John Locke’s by the contemporary philosophers Saul Kripke and Hilary Putnam. They proposed, roughly speaking, that natural kinds are distinguished by the possession of an essence, a property (typically microstructural) that was necessary and sufficient for being of that kind and which gave rise to the many properties commonly associated with that kind. The standard example is water: what makes something water is its molecular structure; that molecular structure, in turn, explains why water (in standard conditions) is clear, potable, a good solvent, and so on. This essentialist model is especially attractive in the context of eugenics, where such microstructural essences would be thought to be a person’s heritable genetic makeup; it also implies a certain picture of our power to change certain behaviors. If, for example, criminal behavior is as inevitable from certain kinds of people as clarity is from samples of (pure) water, then it is fruitless to attempt to reform such people; better to simply change society by breeding them out.

The Individualist Alternative
Eugenic applications aside, one downside for the essentialist approach to natural kinds in biological domains stems from the apparent dearth of appropriate essences. There is currently a debate among biologists and philosophers of science about whether non-essentialist accounts of natural kinds should be developed to handle biological categories — such as species, higher taxa, races, traits — or whether we should instead drop the idea that any of these categories are natural kinds. Perhaps they should be construed instead as individuals — that is, concrete extended objects connected by links of heredity. While the idea may seem strange at first, it connects nicely with standard ways in which biologists think of species as “hunks of the tree of life”. Species would be objectively real in the sense not of being a natural kinds of things (like the elements), but by being cohesively connected by patterns of interbreeding and genetic exchange. This approach maintains the objectivity of the relevant kinds, but deemphasizes their “repeatability”.

With this basic idea in hand, we can apply it at the sub-species level — as some have proposed we consider in thinking about race — by identifying lineages of people which have been relatively reproductively isolated from one another. Galton’s focus on “bloodlines” suggests that eugenicists would have found conceptual resources to exploit in either framework. While the idea that genes or “blood” would play a conceptual role similar to that of a microstructural essence suggests a natural kinds interpretation, seeing humanity as separated into various lineages whose characteristics might be intentionally modified also admits of an individualist treatment.

While the question of how to characterize natural kinds and whether we should view species as individuals or natural kinds have continued to be sources of debate among philosophers, no serious parties to these debates construe these concepts in ways that would vindicate eugenicist doctrine without supplementation by other implausible theses. I have only been attempting to indicate how such concepts could be used as a scaffold for this kind of thoroughly discredited thinking.

-Matthew H. Slater

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