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Wednesday, March 11, 2009

Mereology and species

Laporte on species-kinds and species-individuals

I'm reading Laporte's Natural Kinds and Conceptual Change. On p. 15-16 he talks about how species don't have to be viewed as individuals, and that they can be interpreted as natural kinds. For some reason, he thinks mereology is relevant. Here is the original passage:
Suppose that the organisms of any species make up an individual, or something else that is not a kind. Call such an object a species-individual. Suppose, further, that talk about the species could satisfactorily be interpreted as talk about the species-individual. In that case, I will argue, such talk about the species could also be satisfactorily interpreted as talk about a kind. Here is why: Although the species-individual is not a kind but rather an individual, there is a property, for any such individual, of being part of that individual. For that property, just as for any other property, there is a corresponding kind, such that possession of the property is the essential mark of the kind. Thus, for any species, there is a kind the members of which are preciesely the parts of its species-individual. Call such a kind a species-kind. Because, for any species, there is both a species-individual and a species-kind, there is no reason that discourse about the species would have to be interpreted as being about the species-individual rather than the species-kind.
An example may help to clarify the reasoning. The organisms belonging to Raphanus sativus (and their parts) are precisely the parts of a species-individual. Those parts are precisely the members of a species-kind. Thus the organisms belonging to Raphanus sativus are precisely the members of a species-kind. And it would therefore seem that discourse about the species Rahanus sativus could satisfactorily be interpreted as discourse about that species-kind, whose members are just the organisms of Raphanus sativus. (pp. 15-16)
A few things come to my mind:
  • On Laporte's account, species-individuals seem to be mereological fusions of the species representatives. This is indicated by the claim that the "organisms of any species make up an individual," and by the suggestion that in case of the species-individual of the species Raphanus sativus, "the organisms belonging to Raphanus sativus (and their parts) are precisely the parts of a species-individual".
  • Laporte insists that if it makes sense to speak of species-individuals, it also makes sense of species-kinds. The first problem is, the belief that species are individuals, by itself, does not entail that species-individuals are to be construed as mereological fusions of the species. So, in fact, Laporte's argument, if it works, shows only that (given certain background assumptions about properties) if it makes sense to speak of species-individuals-construed-mereologically, then also it makes sense to speak of species-kinds.
  • The more important problem, however, is that if one really construes species-individuals as mereological fusions, then (at least in classical mereology) it is not the case that being a member of a species is coextensive with beign a part of the corresponding species-individual.
  • Laporte says: "The organisms belonging to Raphanus sativus (and their parts) are precisely the parts of a species-individual" - so far, so good - this means that if you take the fusion of a species, then every representative of this species and every part of such a representative (we might add, and every fusion of arbitrary selection of parts of the species members) is a part of the species-individual.
  • Then he continues: "Those parts are precisely the members of a species-kind." Okay , let's say so (given that we accept the addition in the brackets above). So, for instance, if we take the species homo sapiens, the species-individual, as Laporte construes it, would be the mereological fusion of all humans. Now take the property of being a part of this fusion. This gives you the species-kind. What's important, not only every human being will be a member of this species-kind. Also, every part of a human being will be part of the species-individual, and as such, a member of the species-kind thus construed. Moreover, even the fusion of my left leg and your, dear reader, right hand (assuming you're a human being) will be a member of such species-kind.
  • Now, we can see why it doesn't follow that "the organisms belonging to are precisely the members of a species-kind.". Just like the fusion of my left leg and your right hand is not an organism belonging to homo sapiens, there are fusions of parts of organisms belonging to Raphanus sativus (radish), which are not organisms belonging to Raphanus sativus. Similarly, just like my left foot is not a homo sapiens, even though it is a part of the Laportesque homo-sapiens-individual, there are also parts of the Raphanus sativus-individual, (say a leaf) which are not, buy themselves, organisms belonging to Raphanus sativus.
  • The bottom-line: if you construct species-indvidual as a mereological fusion, you'd better steer clear off classical mereology. Perhaps, a variant of non-classical mereology can be used to make more sense of this, but this requires a lot more work, and prima facie, I don't think there's much hope in this project (I might be wrong though).

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