Cohen might have added, being a functionalist theory in the conventional teleological sense, and the former not. In Cohen's view, what we have in the Darwin/Lamarck dispute are rival theories of why a consequence-explanation holds, not rival alternatives to consequenceexplanation' (ibid.: 271). We see here the import of Cohen's denial that the functionality of explananda is necessary to structural characterization of functional explanation, and the way this connects with his explanation/elaboration distinction. In so far as the functionality of an explanandum enters into a putative causal account, as it does for Lamarck, it does so at the elaborative level. It is not necessary to the formulation of the consequence-laws upon which functional explanation as such rests.
Now, I believe that in this example Cohen mis-states Darwin, and when Darwin's theory is properly expressed, dispositional properties are not essential to explanation. There is a construal within which such dispositional facts’ are non-explanatory precursors of the elongation at issue: and that construal is standard Darwinian theory, at least as I understand it. Let me elaborate. In confronting his imaginary opponent, Cohen attributes to him the view that it is the presence of the trees which explains the elongation of the giraffes' necks, and this is not a dispositional circumstance. Cohen easily rebuts this. But a Darwinian would not, in fact, be likely to advance this argument. He would be more likely to argue in two stages, which Cohen conflates.
First, he would say that the initial appearance of long-necked giraffes is not explained by anything in the environment, dispositional' or otherwise, but by genetic mutation. Such mutations are random, and (pace Lamarckian theories) altogether unconnected with environmental circumstance. It is this mutation which is the cause of longnecked variants initially emerging. And the presence or absence of acacias – importantly - makes it neither more nor less likely that this original adaptive mutation will occur, precisely because mutation is random. Indeed it is perfectly conceivable that the mutation of the neck might not have occurred. Some species, after all, do actually die out. Consider dinosaurs. We cannot then speak here of the operation of a consequence-law (if e would cause f, then e). The presence of acacias cannot therefore be said to dispose'the genes to mutate in an appropriately adaptive way. To suppose otherwise is to fall into the fallacy of reasoning post hoc ergo propter hoc.
Second, our Darwinian would say that the survival of the longnecked variant - a different issue - is undoubtedly then explained, ceteris paribus, by the presence of the trees whose leaves they are better equipped to eat than their short-necked competitors. But dispositional propositions are in no way ‘an essential part of the explanatory story’ at this level of the explanation either. It is rather the case that given the fact of the mutation, the presence of the trees then does sufficiently explain the enhanced survival chances of the long-necked giraffes. That the mutated giraffes can eat acacia leaves, and thus have a competitive advantage in the struggle for survival, in other words remains a totally contingent consequence of their having fortuitously acquired long necks for reasons that are entirely unconnected with the environment or its supposedly ‘dispositional' properties. This can be expressed in standard D-N form, without any recourse to consequence-laws':
LI Individuals well adapted to their environment will have competitive advantages over those less well adapted.
L2 Such advantages, over time, ensure the survival of the fittest’ and thus the generalization through a species of the relevant adaptive features.
CI Some giraffes have long necks as a result of fortuitous genetic mutation.
C2Giraffes live among tall acacia trees.
E Long-necked giraffes have a competitive advantage over short-necked in their natural habitat, and the long-necked variant will therefore prevail.
Certainly the character of the environment is an important part of the explanation of the generalization of long necks among the giraffe population, but not in the way Cohen supposes. Giraffes have long necks not because of the dispositional properties of the environment, but because of the complex interaction through time of genetic variation and environmental circumstance - these two factors, on Darwin's theory (though not Lamarck's) being contingently connected.
An adequate causal account of the acquisition of long necks by the giraffe species would thus have to combine a series of propositions concerning the population dynamics of giraffes, genetic variation in the giraffe population, and features of the environment, including the height of acacias. But none of these propositions would have to be dispositional' for the explanatory story' to make sense, as Cohen alleges. It is not the dispositional fact' that were giraffes to have long necks, they would fare better among the acacias, which in any sense explains why the feature was acquired by some giraffes in the first place, and the explanation of why this variant then prevails supposes this initial acquisition of the feature. Given the mutation, moreover, presence of trees then does sufficiently explain the survival of longnecked giraffes ceteris paribus.
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INTERLUDE: THE GIRAFFES AMONG THE ACACIAS
INTERLUDE: THE GIRAFFES AMONG THE ACACIAS
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