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2. Taxon, Category, and Laws of Nature
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21 Chapter 2 Taxon, Category, and Laws of Nature As pointed out earlier, in the literature on the modern species problem arguably the most fundamental distinction is between species as a taxon and species as a category. Species taxa are particular species and are given binomial names such as Tyrannosaurus rex and Homo sapiens. It is species taxa that evolve, that speciate, that have ranges, that are broad-niched or narrow-niched, and that become endangered or extinct. The species category , on the other hand, is the class of all species taxa. The species problem is typically phrased in terms of determining the ontology of species taxa. But the species category is also a problem. Some conceive of it as an abstract class, a class captured by a definition, the definition determining (or capturing) membership in the class, such that the class (along with its definition) stays the same through time as particular species taxa come and go in terms of existence. Others, however, conceive of the species category not as an abstract class but as a concrete set, simply the set of all species taxa (for examples of both views, cf. Stamos 2003, 150, 258). This latter view, however, that the species category is a set rather than a class, has serious problems typically overlooked by its advocates. Granted, it has greater parsimony, since the species category simply is its member taxa and nothing more. But this view comes at a great cost. For one thing, it cannot possibly capture the sense of the species category remaining the same while its member taxa come and go. If the species category is simply a set, then as a set it changes every time a species taxon comes into existence or goes out of existence. If the species category is viewed as an abstract class, on the other hand, it does not have this problem. Just as with the category gold, which stays the same even though particular atoms of gold come and go in terms of existence, so too, on this view, the species category stays the same even though particular species taxa come and go in terms of existence. But there is a further problem for the view that the species category is a set, namely, that it precludes laws of nature for the species category. It has become a staple of modern philosophy of biology that there are no laws of nature for particular species taxa. There are no laws, for example, specifically for Tyrannosaurus rex. And this absence is exactly what one finds in modern biological literature. Moreover, this observation makes sense from a number of key points. Specifically, a species taxon cannot be the subject of a law of nature because a species taxon gradually evolves. Laws, however , on the usual view of laws, do not change or evolve. The law of gravity , arguably, has not been changing over time, and the same holds true for the speed of light in a vacuum (cf. Nagel 1961, 378–380; Armstrong 1983; Weinert 1995; Stamos 2003, 215–220). But is the species category the subject of laws of nature? This is indeed a very live issue in modern biology. The problem is that if the species category is conceived to be a set, then debate over whether the species category is the subject of laws of nature is immediately shut off. If the species category is a set, then it cannot possibly be the subject of laws of nature because the species category, as a set, is gradually changing over time, whereas laws of nature do not change over time. If the species category is conceived to be an abstract class, on the other hand, then it could possibly be the subject of laws of nature. It need not be the subject of laws of nature, but the possibility is not precluded, given the common view of laws as unchanging. Perhaps the main attraction of conceiving of categories as sets, as nothing more than their members, is that it conforms with a materialist philosophy of nature, according to which what is real is, or is fundamentally, material. My impression is that many scientists (and not just scientists) are typically too materialistic to take seriously the view that abstract categories are part of the fabric of nature. But this should not be considered such a farout view (cf. Weinberg 1992, 46). In cosmology, it is debated among physicists whether the so-called cosmic constants (e.g., the law of...