Sunday, April 30, 2006

Is "only the fittest survive" a tautology?: A Wittgensteinian Take

“One of the best documented examples of natural selection in modern times is the English Peppered Moth. Typically, this moth is whitish with black speckles and spots all over its wings. During the daytime, Peppered moths are well-camouflaged as they rest on the speckled lichens on tree trunks. Occasionally a very few moths have a genetic mutation which causes them to be all black, so they are said to be melanistic. Black moths resting on light-colored, speckled lichens are not very well camouflaged, and so are easy prey for any moth-eating birds that happen by. Thus, these melanistic moths never get to reproduce and pass on their genes for black color. However, an interesting thing happened to these moths in the 1800s. With the Industrial Revolution, many factories and homes in British cities started burning coal, both for heat and to power all those newly-invented machines. Coal does not burn cleanly, and creates a lot of black soot and pollution. Since lichens are extremely sensitive to air pollution, this caused all the lichens on city trees to die. Also, as the soot settled out everywhere, this turned the tree trunks (and everything else) black. This enabled the occasional black moths to be well-camouflaged so they could live long enough to reproduce, while the “normal” speckled moths were gobbled up. Studies done in the earlier 1900s showed that while in the country, the speckled moths were still the predominant form, in the cities, they were almost non-existant. Nearly all the moths in the cities were the black form. It was evident to the researchers studying these moths that the black city moths were breeding primarily with other black city moths while speckled country moths were breeding primarily with other speckled country moths. Because of this, any new genetic mutations in one or the other of those populations would only be passed on within that population and not throughout the whole moth population. Additionally, because the city and country environments were different, there were different selective pressures on city vs. country moths that could potentially drive the evolution of these two populations of moths in different directions. The researchers pointed out that if this were to continue for a long enough time, the city and country moths could become so genetically different that they could no longer interbreed with each other, and thus would be considered distinct species. In this case, what actually happened is that the people of England decided they didn’t like breathing and living in all that coal pollution, thus found ways to clean things up. As the air became cleaner, lichens started growing on city trees again, thus the direction of the selective pressure (birds) was once again in favor of the speckled moths. By now, English cities, as well as countrysides, all have speckled moths, and all are interbreeding at random, thus were not separated for long enough to develop into separate species.”

Let us suppose that contrary to all expectations after the trees of Northern England were no longer covered in soot the black coloured moths continued to thrive at the expensive of the speckled coloured moths. Some have implied that this would be a strike against Darwinian Theory; the theory would have predicted a falsehood, viz., only the fittest survive. I think they are mistaken. Only the fittest survive is not proposition and as such true or false. Rather, survivability is a built in criterion of fitness.

Back tracking a bit, I think we can agree that the reason the speckled coloured moth was expected to resume its original predominance was that it was presumed to be better suited to its environment. In other words, it was presumed to be fitter. Here in lies the problem for opponents of my view. By holding that “only the fittest survive” is like any old proposition they unwittingly run two empirical propositions together, viz., the notion that only the fittest survive and the notion that speckled colouring confers fitness. As a result, they render both unfalsifiable. Indeed, faced with such contradictory evidence one can always insolate one proposition by rejecting the other. Either, the speckled coloured month’s colouring did confer fitness and Darwinian maximum is wrong, or the moths colouring did not confer fitness and the Darwinian maximum still holds.

Conversely, in accordance with what I said above about “only the fittest survive” being a criterion of fitness, I would say that the hypothesis that the speckled coloured moth’s colouring gave it a selective advantage is false. This is also the conclusion I think scientists would draw. By holding out survival as a criterion of fitness we are able to test our predications as to who we think is fit in present day populations (e.g. a population of moths). I suppose we could do something similar using complex computer programs for past populations. Feeding all the information we have about old environments into computer simulation program, we could test various adaptationist explanations.

Before I am dismissed as an adherent of the view that the Darwinian maximum reduces to completely vacuous “only survivors survive”, let me say this. Populations change from generation to generation and often in a particular direction. This is denied by no sane person. The rub for scientists has always been how to account for these changes. There have been many ill fated attempts. Lamarck’s theory of acquired characteristics being passed down to the next generation being the most well known. Darwinians say that “natural selection” can explain at least some of these changes in populations and most people, even creationists, have no trouble conceding that it can (e.g., as in the moth example quoted at the beginning). Darwinian Theory fits with our understanding of genetics and there are powerful mathematical models that explain how selective pressures can change the distribution of any one gene in a given population and at can explain at what rate that change occur. (Of course, these models also explain why artificial selection works) All in all, Darwin has offered up the most coherent and popular theory to date. Where they part ways with many lay people, at least in the States, is that Darwinians believe, as any believer in evolution does, that these changes can eventually lead to speciation.

All that being said, it seems outrageous to say that the success of Darwinian Theory rests on some slight of hand. There is good reason for this. When you really get down to it what Darwinians do is to come up with just so adaptationist stories for why this or that trait or behavior evolved and make predications about survival rates based upon what who they think is fit. As noted, there is nothing suspicious about the latter. As for the former, many are admittedly speculative. However, they are no more mysterious, or on a less academically sure footing than many other historically based fields of endeavor. Moreover, many of the best known evolutionary theorists (e.g., Stephen Jay Gould) reputations rest or rested on their willingness to rein in those who went beyond the available evidence.

Another fundamental misunderstanding concerns the nature of the maximum itself. A statement is tautological in so far as the meaning of the terms are defined by means of each other. In this case, so the argument goes the fittest are those who survive, and those who survive are deemed the fittest. With regards to the famous Darwinian maximum this is false. It only makes sense to talk about fitness in terms of populations that have undergone or are undergoing selective pressures. A segment of the population is fit relative only to another segment of the population that is unfit. If one invokes another mechanism to explain some trait’s dominance, then strictly speaking there is no segment of the parent population that is fitter than any other and consequently it would be inappropriate to describe the offspring (i.e., survivors) of that population undergoing, for example, genetic drift as being fit or not. To think it otherwise leads to the strange conclusion that any Darwinian who wanted to stay true to the maximum would have to avoid ever adopting another evolutionary mechanism.

In coming to this conclusion about the nature of Darwinian maximum, I did not draw my inspiration, Popper, who at one time thought the Darwinian maximum to be a tautology, but rather Wittgenstein. Wittgenstein rejected the Logical Positivist mantra that some propositions are true by definition (e.g. “All bachelors are unmarried men” is true by virtue of the meaning of “bachelor” and “unmarried men”). However, Wittgenstein thought the positivists like so many before them were right to think so called analytic statements were special. He thought, though, they were wrong to think them propositions. According to Wittgenstein such statements are, rather, explicit rules for how to use words (e.g., “All bachelors are unmarried men” rules out the use of word bachelor in the following sentence. “She was a lifelong bachelor.”) Wittgenstein likens these explicit rules to the hum drum rules of grammar. Indeed, he deems them as being part of grammar proper. Like the everyday rules of grammar, they help constitute the bounds of what is sensible and unlike propositions are neither true nor false.

Wittgenstein thought that not all grammatical statements were so easy to pick out. In fact he held that people frequently mistake some grammatical rules as normal propositions (e.g., Sensations are private) When that happens he said, “language goes on a holiday” and the only way “to shew the fly the way out of the fly-bottle” is to investigate, hence the title Philosophical Investigations, the relationships between the offending rule and others parts of language. In Wittgenstein’s case, what such a typical investigation involved was Wittgenstein showing how treating a particular grammatical rule as a proposition leads to absurd conclusions. If successful a cloud of philosophy would be condensed into a droplet of grammar.

If I had to classify “only the fittest survive”, I would say it was a grammatical statement and the absurd conclusion that is avoided by treating it as such is the possibility that sometimes the weakest survive.

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