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causally productive. Thus, populations as a whole, at a given point in time, can
causally produce future states of the same population.
4.1 Non-decompositional Causal Production
Elsewhere, Rob Skipper and I (Skipper and Millstein 2005 ) argue that natural
selection is not a mechanism in Glennan's (or MDC's) senses. So, to some extent
Glennan and I agree. However, the problem is not, as Glennan states, that “the
population as a whole does not interact with other entities as a whole in order to
change its genotype and phenotype frequencies” (Glennan 2009 , p. 335). Indeed,
there is at least prima facie reason to think that populations of water bugs as a whole
often do interact with other entities as a whole. For example, a 1969 study of Sigara
distincta (the organism on which Glennan's water bug example was based) suggests
that an increase in water bugs in a particular location was due to an invasion
(discussed in Macan 1976 ). Here “invasion” is not in the sense of an “invasive
species,” where a few organisms colonize a new area and reproduce rapidly; rather,
it is an invasion analogous to that of an invading army. That is, the water bugs
migrated as a whole, which undoubtedly changed the genotype and phenotype
frequencies in the populations that they migrated from and to. (I give other
examples of populations acting as a whole below.) So again, the problem is not
that the population as a whole does not interact with other entities as a whole in
order to change its genotype and phenotype frequencies.
Rather, one of the reasons that Skipper and I were unable to construe natural
selection as a mechanism in Glennan's sense is that, on his account, the interactions
among the parts of a mechanism are supposed to explain the behavior of the whole.
In other words, mechanistic explanations involve decomposing the whole into its
parts (or entities and activities, on the MDC view). However, if it were the case that a
population could interact with other entities as a whole to produce changes in the
very same population, this would not seem to fit the Glennan and MDC models of
mechanistic explanation: the interactions of the whole would be what explain the
behavior of the whole. In other words, the explanation would not be decompositional
in the way that mechanistic explanations on the Glennan and MDC accounts -
instances of what Skipper and I call the “new mechanistic philosophy” - seem to be.
Here it might be objected that the accounts propounded in the new mechanistic
philosophy are not, in fact, decompositional. 4 After all, Darden argues that “finding
the mechanism for the segregation of genes did not require decomposing genes into
their parts, but required finding the wholes, the chromosomes, on which the parts,
the genes, ride” - in other words, finding the mechanism required going “up” in size
level rather than “down” (Darden 2005 ; see also Darden 1991 ). Glennan, for his
part, has recently given an example of an ephemeral mechanism which occurs “at”
4 Thanks to Carl Craver, Lindley Darden, and Stuart Glennan for each pushing me on this point.
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