“A few million years ago our ancestors were in the trees, with no thought for anything but the next banana. Now we can solve differential equations and send men to the moon. Something happened, but what exactly?” David Papineau NYTimes Book review of The Hand: How its use shapes the brain, language and human culture by Frank R. Wilson.
We might laud the willingness to give all of us credit for moon walks and calculus. Presumably “we” can play basketball like Michael Jordan and compose like Beethoven too. But do we really want natural selection to explain the transition from bananas to ∫ƒ(x)dx? Would Papineau want to argue that some humans from 1000, 10,000, 100,000(?) years ago could not have learned the calculus or played golf on the moon. Without claiming that all human experiences were immanent in early Homo sapiens we might still assert that they would have been capable if properly trained. Do we need natural selection to explain what made a moon walk possible tens of thousands years after humans with the right stuff had evolved?
For many naturalists the incredible fit of organisms to their environment begs for an explanation. This reflects an “awe” factor. It is there in those who see competition everywhere, like Darwin, or those who see cooperation, like Kropotkin, those who see the hand of God or gods and those who insist on no special intervention and every biologist in between whenever we look at the world. It is a powerful common experience across the many camps. This must not be dismissed in part because it can bring together many of the participants. Everyone has favorite examples. Mine are the ways that many flowering plants get insects to help transfer pollen between flowers. An orchid (in the genus Catasetum) uses an amazing spring-loaded device to snap its pollen packet onto the pollinator’s back.
Selectionist explanations come in two modes. In the first, selection is invoked simply to rationalize a situation. Because anything that exists must in some sense have out-survived what has not, we have a survival of the fittest where the fittest are precisely those who survive. This kind of selectionist explanation is too clever for its own good, as any situation you find becomes the inevitable but trivial outcome of selection. It is curious that sociobiology, in the 1970s, and evolutionary psychology, now, have made fealty to this unusually anemic form of Darwinism a litmus test for its champions. To take just one recent example. Steven Pinker holds that the mind is modular and that these modules are optimized organs and gives them a typical selfish genes account. He then proceeds on a forced march of selectionist rationalizations for everything from preference for lawns to fashions. Even if you believe that the brain is modular it does not follow that you must hold that every module is optimized or that there are particular genes for each module or that selectionist accounts ought to be given for every detail of your own preferences.
I am not sure what accounts for this linkage of interest in behavior and the embrace of a caricature version of selection. It may be part of a more general willingness to provide laughably simple explanations for complicated things. I would suggest that any theory of the mind should be at least as complicated as cricket (baseball on my side of the pond). My guess is that minds may be even more complex but this gives us a good starting point and efficiently disposes of shelves of tedious oversimplification. For those popularizers who suggest that they are simplifying only to cut their audience a break I would suggest that given the huge popularity of these sports there is little reason to think that general audiences will not be able to handle at least their level of intricacy.
Selectionism as used by evolutionists aims for more than mere rationalization. In a standard Darwinian account of “natural selection” there must be variance among the objects under consideration, heritability of some of the features and a winnowing of the objects across the generations so that this subset remains to represent the population and reproduce: random variation, heritability and selective retention. When you hear sentences such as “natural selection designed this” or “created that” all of the credit seems to accrue to the selection part of the process. However, laying full credit at natural selection’s door is possible only when (1) the variation is not correlated with the needs of the population, (2) the variation is copious, (3) there is no bias in the process of heritability, and (4) the selection is not carried out with a goal in mind.
Let us take these in turn;
(1) If the variation were correlated with the needs of the organism or population then this process, the skewing of the variants toward good solutions, should get at least some of the explanatory credit.
(2a) If variation of a particular trait is meager, then the short menu of options—the constraints—must get substantial credit for the outcome. Is anyone surprised when they leave a pizza restaurant with pizza? Is it a satisfying explanation to say that presidents and prime ministers are elected simply by popular selection? No. Many factors are involved in providing the limited choice at the polls and any responsible assessment of election results would discuss those as well.
(2b) If variation in one trait is correlated with the variation in another (what Darwin called “correlation of form”) then this non-independence of different traits also deserves to be part of our overall explanation, as a reflection of constraints on possibilities or as a reflection of the byproducts of adaptation.
(3) If the process of inheritance was itself biased, if some gametes were over or under represented ,then this too would get some of the credit that selection would otherwise receive.
(4) If the selection was done with an agenda, as it is done in animal and plant breeding, then the selector should get much of the credit. Should millions of monkeys typing at millions of typewriters get credit for a line of Shakespeare if it takes an observant graduate student to pick out the line? Selection becomes ‘natural selection’ only when there is no breeder making the decisions.
Evolutionists are interested in weighing the various factors just discussed – especially when they are building a selectionist account. A selection only account then is implicitly committed to broad, independent and undirected variance, unbiased heritability, and agenda free selection. These requirements are frequently not met in actual populations. Two important criticisms of pop-adaptationism come from ignoring the menu of possibilities, the dynamics of heritability and the details of selection. These are (1) the problem of looking at traits that are universal in a lineage and (2) the assumption that identifying a trait’s function warrants the conclusion that a selection-only account is sufficient to explain it’s presence.
Apportioning credit for the evolution of a trait is itself an intricate exercise. In the case of two proteins we could imagine counting up the number of amino acids and, if we knew everything, identify a subset of the shared residues that are the same due to common ancestry, others that are the same due to random mutation and drift and finally some that are the same thanks to functional constraint and selection. Even in this example (where judging sameness is unambiguous, amino-acids either match or they do not) it is difficult to imagine that we would know enough to confidently partition the explanation into these factors. This example highlights another important feature of partitioning credit. We must be comparing specific traits. It simply does not make sense to ask us to apportion credit in general - we need to provide a richer context for this question. The protein example is useful because we can talk in terms of absolute number of amino acids, behaviors and morphology will be much more since they are difficult to understand at this level of resolution. Another way to illustrate this point is to ask, what percent of a feather is due directly to selection?
Selectionist accounts have been used in immunology (production of the B-cell receptor repertoire), development (emergence of the cortical spatial map in amphibian and mammalian eyes), dynamics of ideas in society (memes), epistemology (dynamics of theory choice), economics (evolution of firms). These approaches would all benefit from a careful examination of the source and breadth of the variation, the mechanism of transfer (heritability) and the details of the selective agent.
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