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The Philosophical Status of Natural Selection http://pages.towson.edu/scully/philosophical.html

It may seem odd to have a section on Philosophy in a set of notes designed for a science course, but that is only because, for historical reasons unknown to me, the people who know the least about the philosophy of science are scientists themselves.

Evolutionary Biology is full of philosophical issues. First, because Darwinian evolution requires a substantial change in the way we view the world around us. Second, unlike mathematical theories in the physical sciences, the foundation of evolutionary biology is based on verbal arguments, and with such arguments come semantic questions, which, in turn, seem to draw philosophers the way that some flowers attract honeybees. Finally, there are the implications of evolutionary biology with respect to our own species, and what some view as new set of principles to govern our lives.

The Tautology Issue

"This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest." .....Charles Darwin, The Origin of Species, 1859.

In choosing a phrase to summarize his theory of Natural Selection Charles Darwin unknowingly supplied grist for the mills of philosophers of science for at least the next 130 years. Because it is a verbal model of a major process of the material world, Natural Selection is far more vulnerable to semantic and philosophical criticism than a mathematical scientific system such as, for example, Einstein's General Theory of Relativity. There is a vast amount of material on this issue running from articles by biologists and philosophers to articles in general magazines and discussions in books by religious opponents to evolutionary biology (i. e., the fundamentalist Christian "creation-science" movement) (see Kitcher, 1982; Sober, 1984).

The problem arises with the definition of fitness. If fitness is defined in terms of mere survival, then "survival of the fittest" becomes "survival of those who survive". This rephrasing not only sounds circular and almost meaningless, but it is also hard to imagine how it could be used to explain anything in the natural world or generate scientifically testable predictions. The key philosophical point is that, phrased in this way, the idea of natural selection becomes a tautology. A tautology in philosophy is a simple logical truth; for example, the general statement "P or not P", where P is some proposition (e. g., snow is white or it is not white). There is nothing wrong with tautologies, per se - it is just that they are poor foundations for scientific theories. The tautology issue is almost entirely based on the phrase "survival of the fittest", and it has been blown out of proportion to the point that it has been argued that if natural selection is a tautology, then all of evolutionary biology collapses because of an invalid conceptual foundation (Sober, 1984). However, the tautology issue becomes meaningless when you examine Darwin's logical argument for natural selection in which there is a lot more to it than just survival. Second, is the fact that fitness is actually a combination of viability (survival from conception to adult) and fertility (expected number of offspring), which R. A. Fisher extended to the expected number of offspring who survive to reproduce in turn. However, this doesn't resolve the issue completely because natural selection is still being defined in terms of its effect.

Stephen Jay Gould, among others, has suggested (see "Darwin's Untimely Burial" in Gould, 1977) that the solution to the problem is to look for measures of fitness which are independent of survival. For example, you could do an engineering style analysis of an organism's morphology, physiology, and behavior in order to predict its likelihood of escaping an attack by a predator. This is exactly the kind of analysis that evolutionary biologists strive to accomplish. As Elliott Sober (1984) put it: "Fitness is a probabilistic disposition (a propensity) to survive and be reproductively successful. It is connected with actual reproductive success the way a coin's bias is connected with actually landing heads more often than tails".

An analogy might help to clarify things at this point. I'm sure that almost everyone would agree that a successful corporation is one with a high profit margin. However, if you wanted to determine why a corporation was successful you wouldn't go back to the annual report to the stockholders. Instead, you would examine the company's combination of investment, management, marketing, and production strategies in order to determine why the company made a good profit. Charles Darwin may have used an oversimplified phrase to summarize natural selection, but neither he nor any evolutionary biologist since thought that it accurately summarized the evolutionary process.


The Question of Testability

The testability issue is in part related to the question of whether or not natural selection is a tautology. In this version, the basic argument is that because the process (natural selection) is defined by its effect (survival) the fundamental circularity of the concept renders it impossible to examine via accepted scientific methods. I have already discussed the tautology issue, but it should be clear from the formulation of natural selection by Darwin that every point within the sequence is amenable to independent, experimental verification. What more could any good empirical reductionist want?

The person often cited in a philosophical discussion of the testability issue is Sir Karl Popper. Popper is a world famous philosopher of science, who tried to articulate the process by which science advances our knowledge of the material world. Starting with his book, Logic of Scientific Discovery (1934), he developed a restrictive criterion for what constitutes a valid scientific hypothesis. Briefly, an hypothesis is only valid if one can conceive a way in which the hypothesis could be falsified by some empirical test. Thus the hypothetico-deductive method, used by Darwin and Wallace in developing the theory of natural selection, falls outside the realm of Popper's scientific philosophy. Popper's most famous comment about natural selection came in his 1976 book, Unended Quest: an Intellectual Autobiography, when he said: "I have come to the conclusion that Darwinism is not a testable scientific theory, but a metaphysical research programme - a possible framework for scientific theories." (Note: it is clear from the context of this quote that Popper was equating Darwinism with natural selection). So, it would seem, natural selection is not a scientific theory, but rather some type of conceptual hypothesis generating machine.

Popper's argument was almost entirely based on the tautology issue, and he later admitted that he had not appreciated the basic argument of natural selection. Furthermore, he retracted his statements in later publications and agreed that natural selection was as valid as any other scientific theory (Sonleitner, 1986). However, some authors still cite Popper's earlier statements on natural selection, then equate evolution with natural selection, and conclude that the whole of evolutionary biology lacks any scientific validity.

The second aspect of the testability issue can be summarized as the idea that because natural selection appears to explain so much it really explains nothing! This argument, most clearly set forth by Stephen Jay Gould and Richard Lewontin (1979), criticizes not natural selection, but an overapplication of the concept. They argue that evolutionary biology is full of untested scenarios where a particular biological phenomenon is explained as a direct result of natural selection. They argue that this "adaptationist programme", which explains everything as a result of natural selection, is overly reductionist and ignores the fact that organisms are integrated systems. In other words, some characteristics either may not be adaptive, or, at the very least, not the direct result of natural selection. Other authors argue that, while these criticisms may be true, the analysis of specific characteristics from the perspective of adaptations is still the most fruitful mode of analysis (Mayr, 1983), the use of optimization theory is still valid (Maynard Smith, 1978; Stephens & Krebs, 1986 - Chap. 10), and there is nothing wrong with the reductionist approach when it is applied properly (Williams, 1985). Nevertheless, all authors agree that any phenomenon should be examined with multiple working hypotheses, including ones that do not invoke natural selection as the immediate cause of particular characteristic.

Natural Selection, Morality, and the Individual

Darwinian evolution was opposed on a number of grounds when it was first introduced because it either threatened the religious views of some people, or it did not appeal to those who wanted an orderly, deterministic universe with no random components. On the other hand, there were those who saw Darwinian evolution, and natural selection in particular, as the perfect justification for their philosophical views. People as different from one another as Henry Ford and Karl Marx have believed that their views were supported by Darwin's theory.

Darwin was well aware of the philosophical implications of his work (Gruber & Barrett, 1974), and one of his staunchest supporters, T. H. Huxley (called by some, "Darwin's Bulldog"), wrote a book entitled Evolutionary Ethics. However, you must realize that science can only deal with natural, material phenomena. What some philosophers, and also some scientists, choose to interpret as the philosophical implications of scientific findings is as far outside the realm of science as any other metaphysical issue. This is not to argue that science is "value free" (after all, it is done by human individuals each of whom has his or her own philosophical baggage), or that scientific findings do not have ethical implications (e. g., those raised by genetic engineering); I mean that such issues are outside of the scientific process per se.

A relatively simple example may help at this point. There are perfectly sound evolutionary reasons why, in a dioecious species, males should be promiscuous and females should be cautious in mate selection. However, this fact in no way supports the philosophical attitudes found in Playboy magazine, polygamy, monogamy, or any of the other myriad systems related to mating that are found in human societies. Each of these is based more on individual or social moral choices than any reading of the Origin of Species. Just as we have developed techniques to treat genetic diseases, we have built social and philosophical systems that either go beyond the underlying biological constraints or ignore them entirely. Still, there are some religious and philosophical issues related to evolutionary biology, and for these I recommend books like those by Kitcher (1982) and Ruse (1986).


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