In Chapter 6, Many are called but few are chosen: the problem of ‘selection for’, Fodor and Piattelli-Palmarini (F&P-P) launch their ‘conceptual’ assault on the theory of natural selection.
The chapter begins with a review of Stephen Jay Gould and Richard Lewontin’s ‘iconic’ 1979 paper: The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. This is where Gould and Lewontin attack what they saw at the time as a pervasive methodology of evolutionary explanation:
It is based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an organism into unitary “traits” and proposing an adaptive story for each considered separately. [Stephen Jay Gould and Richard Lewontin, 1979]
Gould has elsewhere described these adaptive stories as ‘just-so stories’:
Evolutionary biology has been severely hampered by a speculative style of argument that records anatomy and ecology and then tries to construct historical or adaptive explanations for why this bone looked like that or why this creature lived here. These speculations have been charitably called “scenarios”; they are often more contemptuously, and rightly, labelled “stories” (or “just-so stories” if they rely on the fallacious assumption that everything exists for a purpose). [Gould, S.J. 1980. From: ‘Introduction’ to Björn Kurtén, Dance of the Tiger: A Novel of the Ice Age. N.Y.: Random House.]
In their 1979 paper Gould and Lewontin illustrate their argument by contrasting the arches which hold up (eg) the great central dome of St Mark’s Cathedral in Venice with the spandrels, which are the tapering triangular spaces where two rounded arches intersect at right angles.
The architects chose to build the arches, because it’s the arches which hold up the dome. They didn’t choose to build the spandrels. No matter how ornately the spandrels were decorated, they are only there because the arches are there. They came along for the ride. Gould and Lewontin’s lesson to evolutionary biologists was not to assume everything in nature is an arch and therefore has a functional explanation. Some things are spandrels – free-riders:
One must not confuse the fact that a structure is used in some way [eg the mosaics or paintings adorning a spandrel]… with the primary evolutionary reason for its existence and conformation. [Stephen Jay Gould and Richard Lewontin, 1979]
But the spandrels warning doesn’t go far enough for F&P-P. For them it’s not just that some adaptationist stories are false, it’s that ‘there is something wrong at the core of adaptationism’ per se.
F&P-P’s next move is to introduce counterfactuals, by way of the old chestnut about the function of the heart. (I’ve talked about this already, in Not thumping but pumping, in the context of Stuart A Kauffman’s Reinventing the Sacred.)
We know when something is a functional feature (arch) or a free-rider (spandrel) by asking counterfactual questions. If architects had been able to build arches without spandrels would they still have built arches? Yes. If architects had been able to build spandrels without arches would they still have built spandrels? No.
Or in the case of the heart, which pumps blood but also makes heart noises:
[T]he counterfactual whose truth or falsity decides the issue is: if there could have been blood pumps without noises Mother Nature would probably have selected them, but not vice versa.
F&P-P leave this thought dangling while they dart back into the psychology of learning. They give the example of an animal trained by reinforcement to respond to yellow triangles. Now you want to know what the animal has actually learned: to respond to yellow things of any shape, or to triangles of any colour?
The answer is to apply John Stuart Mill’s ‘method of differences’. Design an experiment to train the animal to discriminate yellow triangles from (say) blue squares, then test if the animal responds to blue triangles or yellow squares, when offered a choice:
Roughly, if the creature’s training generalises to blue triangles (but not to yellow squares), then what it learned … was to respond to triangles; if it generalises to yellow squares (but not to blue triangles), then what it learned … was to respond to yellow things.
…[T]he ‘what is learned’ problem [is another] free-rider problem: when a yellow triangle is the [reinforced stimulus], does conditioning to yellow free-ride on conditioning to triangularity, or is it the other way round?
…What the adaptationist wants to know is: What would happen if the de facto coextension of arches and spandrels breaks down; which would the architect have selected-for if he had been offered arch-free spandrels on the one hand, or spandrel-free arches on the other? … The logic of the situation remains the same whether it’s an architect or Mother Nature or some psychologist who is doing the selecting; and it’s likewise independent of whether it is the organism’s phenotype that is being selected-for or its behavioural repertoire. …[S]election-for problems need to appeal to counterfactuals if they are to distinguish between coextensive hypotheses…
…[J]ust as adaptationist evolutionary theory has a problem about distinguishing the trait selected for from its free-riders [eg in the case of the heart which both pumps and makes thumping noises], so learning theory has a problem when it attempts to distinguish the ‘effective’ stimulus property from its more correlates.
F&P-P think that Gould and Lewontin are entirely right that
a theory of natural selection must somehow allow for the possibility of phenotypic traits that are not adaptations.
But they reckon Gould and Lewontin missed the more profound significance of their warning:
[O]nce the character of selection-for problems is properly understood, it becomes apparent that the question that phenotypic free-riding raises cannot be answered within the framework of adaptationist theories of evolution.
The more profound significance is, according to F&P-P, that in the context of natural selection you cannot tell what is an arch and what is a spandrel. If the pumping action of the heart and the thumping noise it makes are always coextensive, you cannot tell which of those features the heart was selected for. We may think we can settle the issue by appeal to counterfactuals: if the heart pumped without thumping; or if it thumped without pumping. But for F&P-P this is not legitimate:
How could selection be sensitive to the consequences of counterfactually removing [pumping] but not [thumping] (and/or the consequences of counterfactually removing [thumping] but not [pumping]) if, in point of fact, neither [pumping] nor [thumping] actually is removed? Selection cannot, as a matter of principle, be contingent upon (merely counterfactual outcomes.
…[T]he outcomes of merely counterfactual events cannot exert selection pressures… The number of rabbits in Australia is unaffected by the number of foxes in England. That’s because the predations of the one on the other are all merely counterfactual, and possible-but-not-actual events do not exert selection pressures.
Can this argument possibly be sound?
It seems to me that F&P-P have been so dazzled by the prospect of uprooting modern biology that they have completely missed the wood for the trees.
But that’s for next time.
© Chris Lawrence 2011.