• Email
  • Single Page
  • Print

Not So Natural Selection

Second, Fodor and Piattelli-Palmarini point out that there are molecular interdependencies that arise from the fact that genes are organized onto long thread-like chromosomes. The translation of a gene that is the first step in the process of producing a protein is sensitive to changes in DNA that is nearby on the chromosome strand, so that several genes of quite different specificity can be affected by the same change in the chromosome.

Third, the organization of genes onto the chromosomes in the cell means that when an offspring has inherited a particular form of one gene from a parent, it will also, with high probability, inherit the forms of a number of other genes that lie nearby on the same chromosome strand in that parent. It takes many generations for such historical linkages between genes on the same chromosome to be dissolved. Therefore selection on one function may result in inherited changes in other functions.

While Fodor and Piattelli-Palmarini put considerable weight on these actual functional interactions in organisms, the main issue for them has to do with how we describe the actual objects of selection. If we are to describe what is going on in nature as “natural selection,” then we must remember that it is not traits that are selected but organisms; the traits they possess as properties will determine what their contribution will be to the next generation. This is not an idle distinction because organisms will be “selected” as a consequence of their total biology. In our example we say that dark-colored mice are selected over light-colored mice. But not all dark-colored mice are candidates for natural selection because some of them might be sterile, or have a poor sense of smell, or any other of a vast list of properties that organisms may possess, and those properties may work against the survival of their offspring and thus their natural selection.

Moreover, an alternative way that selection might have acted is by selecting mice that were active only after dark when the predators could not see them, in which case color would be irrelevant. The fact that no such mice happened to exist at the time certainly does not rule out that they might have come into existence. Thus, to give a correct description of the objects of selection we would have to say that what was selected were mice that were dark-colored and not nocturnal. But suppose the mice could make a loud screaming noise that would frighten away predators. Then too, their color would be irrelevant so the correct statement is that what was selected were mice that were dark-colored and not nocturnal and made squeaky noises. We cannot stop there. According to Fodor and Piattelli-Palmarini our specification of what kind of mice were selected properly includes an infinite number of descriptors that take into account all the actual properties of our selected mice. This logic would then include that the mice are smaller than Manhattan.2

The authors are driven to this by a logical necessity because we must, in fact, implicitly take into consideration why it was mice of a certain coat color and not, say, of a particular diurnal activity that were selected. If we are to understand the actual path of evolutionary change, the lack of variation in certain traits is of as much importance as the presence of variation in others. In fact, it often happens that artificial selection in the laboratory for a particular trait when replicated in different genetic strains results, in addition to the trait being directly selected, in different changes in other characteristics in the different lines. This is because in different strains genetic variation for different hitchhiking traits is present on the same chromosome as the genes influencing the directly selected trait.

One way to escape from the logical necessity of an impossibly complete specification of the actual living objects that are selected is to stop talking about “selection for” certain kinds of organisms and refer only to “selection of” the trait or traits that actually change as a result of the process of differential reproduction.3 It is certainly true in artificial selection experiments that you don’t always get what you asked for and there is no reason why the differential reproductive success in nature of different types that we call “natural selection” should not produce the same result. This alternative, however, will make most evolutionary biologists very uncomfortable, because they want to provide narratives of what is really happening to the different sorts of creatures in nature.

A major issue to which Fodor and Piattelli-Palmarini give insufficient attention is the concept of “adaptation.” They point out, correctly, that every living creature must be in some sort of adaptive correspondence to its conditions of life or else it would be dead, so the fact of apparent adaptation of living organisms to the world they inhabit is hardly a surprise. But the “adaptation of organisms to their environment” is a characterization of the relation between organism and environment that misses half the story. It is based on the metaphor of the “ecological niche,” a preexistent way of making a living into which organisms must fit or die. But there is an infinity of ways that organisms might make a living, an infinity of ways of putting together the bits and pieces of the external world. Which of these is an “ecological niche”? The only way to tell is if some organism makes a living in that way. Just as there is no organism without a niche, there is no niche without an organism. A famous example of how niches are defined by the organisms that inhabit them comes from the attempt to find life on Mars. How does one detect life on Mars? One suggestion was to send up a sort of microscope, collect some dust from the Martian surface, and see if anything wiggled. If it wiggles it is alive. This seemed too unsophisticated for the space scientists.

Instead they sent up a sort of vacuum cleaner filled with a nutrient solution containing a radioactively labeled simple sugar. If the dust sucked up from the surface contained living cells, they would start to grow and divide, metabolize the sugar, and release radioactive carbon dioxide, which would be detected by a counter. The Mars lander never detected any life activity although it was determined to be in perfect working order. But that does not mean that there is no life on Mars. It means that there is no life in Martian dust that grows on the sort of sugar provided. This device certainly would not have detected a science-fiction Martian. What the space scientists had done was to provide an ecological niche for a specific kind of life that they knew from earth, a niche that does not match a vast variety of earthly organisms. If you do not specify the kind of organism you are looking for you cannot specify its ecological niche. Perhaps the space program should look again for wiggly things.

Fodor and Piattelli-Palmarini do not discuss the fact that every kind of organism, as a consequence of its life activities, reforms the world around itself and creates its own “ecological niche” that is in constant flux as the organism behaves and metabolizes. Organisms do not “fit into” niches, they construct them, and biologists’ realization of this fact has led to the creation of theories of “niche construction.”4 It is not simply that birds and ants build nests or humans build houses. The metaphor of “construction” covers a number of activities of metabolizing creatures that create the world around themselves. Plants, putting down roots, change the physical structure of the soil in which they are growing and they extrude into the soil chemicals that encourage the growth of certain fungi. These molds, far from “infecting” the plants, form intimate connections with the roots that are a pathway for substances that promote plant growth.

In a great variety of organisms the chance of survival and the growth rate of individuals are not the highest at the lowest population density, but at intermediate numbers. Fruitflies, in their immature worm stage, for example, are farmers. They eat yeast that grows on the surface of the decaying fruit on which they live. The worms burrow into the fruit and the yeast grows on the linings of these tunnels. So, up to a point, the more worms, the more tunnels; and the more tunnels, the more food. Animals and plants create storehouses of energy on which they call in nonproductive times. Bees store honey and squirrels store acorns. Humans store grain and, in modern times, have a commodity futures market, so that affordable bread is available in the winter.

The most remarkable feature of terrestrial organisms is that each one of them manufactures the immediate atmosphere in which it lives. By use of a special kind of optical arrangement (Schlieren optics) on a motion picture camera it is possible to see that individual organisms are surrounded by a moving layer of warm moist air. Even trees are surrounded by such a layer. It is produced by the metabolism of the individual tree, creating heat and water, and this production is a feature of all living creatures. In humans the layer is constantly moving upward over the body and off the top of the head. Thus, organisms do not live directly in the general atmosphere but in a shell produced by their own life activity. It is, for example, the explanation of wind-chill factor. The wind is not colder than the still air, but it blows away the metabolically produced layer around our bodies, exposing us to the real world out there.

The appearance of Fodor and Piattelli-Palmarini’s book at this time and the rhetoric and structure of its argument are guaranteed to provoke as strong a negative reaction in the community of evolutionary biologists as they have among philosophers of biology. To a degree never before experienced by the current generation of students of evolution, evolutionary theory is under attack by powerful forces of religious fundamentalism using the ambiguity of the word “theory” to suggest that evolution as a natural process is “only a theory.” While What Darwin Got Wrong may have been designed pour ĂŠpater les bourgeois and to forcibly get the attention of evolutionists, when two accomplished intellectuals make the statement “Darwin’s theory of selection is empty,” they generate an anger that makes it almost impossible for biologists to give serious consideration to their argument.

Conscious that Fodor and Piattelli-Palmarini may have overdone it, they have circulated an essay that assures evolutionary biologists that they are not challenging the basic mechanism of evolution as a natural process described by the four principles of variation, heredity, differential reproduction, and mutation. In particular, they reject any notion that natural selection is some sort of “force” with laws like gravitation. For them, natural selection is simply a name for the differential reproduction of different kinds in a population. Not to be misunderstood, perhaps biologists should stop referring to “natural selection,” and instead talk about differential rates of survival and reproduction.

The other source of anxiety and anger is that the argument made by Fodor and Piattelli-Palmarini strikes at the way in which evolutionary biologists provide adaptive natural historical explanations for a vast array of phenomena, as well as the use by a wider scholarly community of the metaphor of natural selection to provide theories of history, social structure, human psychological phenomena, and culture. If you make a living by inventing scenarios of how natural selection produced, say, xenophobia and racism or the love of music, you will not take kindly to the book.

Even biologists who have made fundamental contributions to our understanding of what the actual genetic changes are in the evolution of species cannot resist the temptation to defend evolution against its know-nothing enemies by appealing to the fact that biologists are always able to provide plausible scenarios for evolution by natural selection. But plausibility is not science. True and sufficient explanations of particular examples of evolution are extremely hard to arrive at because we do not have world enough and time. The cytogeneticist Jakov Krivshenko used to dismiss merely plausible explanations, in a strong Russian accent that lent it greater derisive force, as “idel specoolations.”

Even at the expense of having to say “I don’t know how it evolved” most of the time, biologists should not engage in idle speculations.

Letters

What Darwin Got Wrong’ September 30, 2010

  1. 2

    This logical result is pointed out by the philosophers Ned Block and Philip Kitcher in “Misunderstanding Darwin,” their review of Fodor and Piattelli-Palmarini’s book, Boston Review, March/April 2010.

  2. 3

    This suggestion was made by the philosopher of biology Elliott Sober, in response to an earlier version of Fodor’s argument. The general tone of argument among philosophers can be judged by the title of Sober’s paper in Mind and Language, Vol. 23, No. 1 (February 2008): “Fodor’s Bubbe Meise Against Darwinism.”

  3. 4

    A recent book on the subject is Niche Construction by John Odling-Smee, Kevin N. Laland, and Marcus W. Feldman (Princeton University Press, 2003).

  • Email
  • Single Page
  • Print