Extinction as an Argument for the Effectiveness of Natural Selection

Natural selection is differential reproduction due to varying fitness. According to evolutionary epistemology, cognitive abilities raise fitness; therefore selection works for better cognition, at least in cases where such improvements are available, useful, and not too expensive.

The fact that man survived evolution under competition makes plausible the reverse conjecture: Our cognition cannot be too bad. This inverted argument is not altogether compelling. But by this argumentative step we may justify our (limited) trust in our cognitive apparatus.

What testifies the effectiveness of natural selection? Usually the multiplicity of species counts as the best argument. Wasn't it the different finches on the Galapagos Islands which aroused in Darwin the idea of natural selection? And if we are told that there exist on earth at least five million, possibly even twenty million different kinds of organisms (not to count bacteria or viruses), all occupying their own ecological niches, then we are even more easily convinced of the effectiveness of natural selection.

But again there is an objection: Could there not be several, even many, ways to put up with the same environmental conditions? Could not totally different species occupy the same ecological niche? Is it then a question not of natural selection, but of mere chance which species are formed and populate the earth?

There are in fact arguments supporting this interpretation. We have concrete cases where similar ecological niches are occupied by completely different species: The niche of the great pasture animals is occupied in the savannas of Africa by hoofed animals, in Australia by kangaroos. According to the neutral theory of evolution, developed since 1968 by Motoo Kimura, many genetic changes follow pure chance processes.

Again, there is a better argument for the effectiveness of natural selection: the extinction of species. For that, we must only recall how many species did already die out. Evolutionary biologists take the number of extinct species to be at least one hundred times that of the existing ones. Why did so many species die out?

As with individuals it happens occasionally that species get extinct more or less accidentally, by a flood, by the outbreak of a volcano, or by the impact of a meteorite. As with individuals, we might talk here of situational death. It would be absurd, however, to book all extinctions under situational death. In contradistinction to individual aging and dying, there is, as far as we know, no preprogrammed species extinction. Thus, we must look for external causes in most cases. Hence we might also ask: What makes organisms, populations, species fail?

For selectionists the answer is simple: Populations and higher taxonomic units die either because they cannot put up (any more) with environmental conditions, first of all if these conditions change relatively fast, or because they are displaced by fitter organisms, possibly by superior members of the same species. Both cases instantiate mechanisms of natural selection.

And how do antiselectionists, e.g. neutralists, explain species extinction? Not at all. The reason is not that they couldn't cope with the term ‘extinction'. That species become extinct, even antiselectionists can state and find in need of explanation. However, they cannot offer a plausible explanation. The theory of natural selection has higher explanatory power than any antiselectionist theory, say the neutral theory.

Selection theories not only explain the success, but also the failure of species. Again, there is a pronounced asymmetry: For success several explanations are thinkable, but not for failure. The failure of species is therefore a much better argument for the theory of selection, presumably the best one.

It should be evident by now why we made this side-step to biology, to evolution, to the extinction of species, and to the explanatory power of natural selection: The arguments have the same structure, they are isomorphic. In neutral terms the argument reads: The best argument for realism/for natural selection is not the success of scientific theories/of organic species, but rather the failure of so many others. And if we accept this analogy, we may even admit that the argument for realism and the argument for natural selection support each other. That's why we made this side-step to biology. And if we accept this mutual support, we may even take it as a further argument A14 for realism.