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Darwin’s Revolution

A second difficulty of both Futuyma’s analysis and the Kitchers’ is that they lose courage on the question of materialist explanations of the world. In the last chapter of Abusing Science, the Kitchers offer a Newtonian first cause as a form of religious belief that is not in necessary conflict with natural science. God, according to this view, set the world rolling according to laws of His own invention and has since kept His hands off. The job of natural sciences is then to explicate the divine order. But that analysis misses the essential differences between a God who has not intervened (except perhaps to produce an occasional incarnation or resurrection) and a god who cannot intervene. Nature is at constant risk before an all-powerful God who at any moment can rupture natural relations. For sufficient reason, He may just decide to stop the sun, even if He hasn’t done so yet. Science cannot coexist with such a God. If, on the other hand, god cannot intervene, he is not God; he is an irrelevancy. By failing to confront this problem, biologists and philosophers may make Unitarians and agnostics feel that ontological pluralism is a happy solution, but they haven’t fooled any fundamentalists, who know better.

If Darwin’s revolution was not in proclaiming evolution as a fact, then it must have been in his theory of its mechanism. And what was that theory? Why, “natural selection,” of course, which then makes the theory of natural selection the very essence of Darwinism and any doubt about the universal efficacy of natural selection anti-Darwinian. There is a form of vulgar Darwinism, characteristic of the late nineteenth century and rejuvenated in the last ten years, which sees all aspects of the shape, function, and behavior of all organisms as having been molded in exquisite detail by natural selection—the greater survival and reproduction of those organisms whose traits make them “adapted” for the struggle for existence. This Panglossian view is held largely by functional anatomists and comparative physiologists who, after all, make a living by explaining what everything is good for, and by sociobiologists who are self-consciously trying to win immortality by making their own small revolution. Evolutionary geneticists, on the other hand, who have spent the last sixty years in detailed experimental and theoretical analysis of the actual process of evolutionary change, and most epistemologists, take a more pluralistic view of the forces driving evolution.

An occasional philosopher has allied himself or herself with the “adaptionists,” who give exclusive emphasis to natural selection, and, one such, Michael Ruse, makes a characteristic presentation in Darwinism Defended. Darwinism, the representative of objective modern science, is under ideologically motivated attack. Professor Ruse is alarmed: “‘Darwinism,’ as I shall refer to Darwin-inspired evolutionary thought, is threatened from almost every quarter.” Well, not from every quarter, just the right and left flanks, it seems. First, the fundamentalists, supported by Ronald Reagan, make a know-nothing assault from the right. No sooner have real evolutionists wheeled to face this attack than they are fallen upon by subversive elements from the left, “biologists with Marxist sympathies” and their “fellow travelers” among philosophers who argue “that any evolutionary theory based on Darwinian principles—particularly any theory that sees natural selection as the key to evolutionary change—is misleadingly incomplete.”

On to the field, mounted upon his charger perfectly adapted for the purpose, with weapons carefully shaped by selection to spread maximum confusion among the enemy, not to mention innocent civilians, comes Professor Ruse, “trying to rescue…from the morass into which so many seem determined to drag them,” “Darwin’s life and achievements.” In all fairness to Professor Ruse, he did not invent this version of events. The theory that evolutionary science is being brutally beaten and cut with crosses, hammers, and sickles made its first appearance in E.O. Wilson’s On Human Nature as the only plausible explanation he could imagine for the failure of sociobiology to achieve instant, universal, and lasting adherence. The situation of evolutionary theory, however, is rather more complex and more interesting than Professor Ruse’s Manichaean analysis suggests.

There are two basic dynamic forms for evolving systems. One is transformational, in which the collection of objects evolves because every individual element in the collection undergoes a similar transformation. Stellar evolution is an example. The universe of stars is evolving because every star undergoes the same general set of transformations of mass and temperature during its life cycle from birth to its eventual winking out. The Harvard class of 1950 is getting grayer and flabbier, because each of its members is doing so. Most physical systems and social institutions evolve transformationally, and it was characteristic of pre-Darwinian evolutionary theories that they, too, were transformational. Lamarck held that a species evolved because its individual members, through inner will and striving, changed to meet the demands of the environment.

The alternative evolutionary dynamic, unique as far as we know to the organic world, and uniquely understood by Darwin, is variational evolution. In a variational scheme, there is variation of properties among individuals in the ensemble, variation that arises from causes independent of any effect it may have on the individual who possesses it. That is, the variation arises at random with respect to its effect. The collection of individuals evolves by a sorting process in which some variant types persist and reproduce, while others die out. Variational evolution occurs by the change of frequency of different variants, rather than by a set of developmental transformations of every individual. Houseflies, for example, have become resistant to DDT. Because of random mutations of genes that affect the sensitivity of flies to insecticide, some flies were more resistant and some less. When DDT was widely applied, the sensitive flies were killed and their genes were lost, while the resistant forms survived and reproduced, so their genes were passed on to future generations. Thus, the species as a whole became resistant to DDT.

Darwin’s problem, and that of anyone trying to produce a theory of evolution, was to explain two apparently distinct features of the organic world, diversity and fit.

In considering the Origin of Species, it is quite conceivable that a naturalist…might come to the conclusion that species had not been independently created, but had descended like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which justly excites our admiration.7

The observations of diversity were strong support for evolution, for the immense variety of species alone seemed to make special creation unreasonable. Once, when J.B.S. Haldane was asked what he could deduce about the Creator from the nature of Creation, he replied, “He must have been inordinately fond of beetles.” The marvelous fit of organisms to their environments, however, seemed evidence of a deliberate design. What was so attractive about Darwin’s theory was that it explained both diversity and “that perfection…which so justly excites our admiration” by a single coherent mechanism.

Darwin claimed that it was the sorting process among variants that produced the fit of organisms to the environment. In the “struggle for existence,” some variants, because of their particular shapes, behaviors, and physiologies, were more efficient at using resources in short supply, or in escaping predators or other vicissitudes of nature. Thus, the differential survival and reproduction of different variants would be directed by the circumstances of the external world; and so the outcome of the sorting process would bear a close correspondence to that world and its demands. That is, adaptation of the species occurs by sorting among individuals. What vulgar Darwinists fail to understand, however, is that there is an asymmetry in Darwin’s scheme. When adaptation is observed, it can be explained by the differential survival and reproduction of variant types being guided and biased by their differential efficiency or resistance to environmental stresses and dangers. But any cause of differential survival and reproduction, even when it has nothing to do with the struggle for existence, will result in some evolution, just not adaptive evolution.

The Panglossians have confused Darwin’s discovery that all adaptation is a consequence of variational evolution with the claim that all variation evolution leads to adaptation. Even if biologists cannot, philosophers are supposed to be able to distinguish between the assertion that “all x is y” and the assertion that “all y is x,” and most have. This is not simply a logical question but an empirical one. What evolutionary geneticists and developmental biologists have been doing for the last sixty years is to accumulate a knowledge of a variety of forces that cause the frequency of variant types to change, and that do not fall under the rubric of adaptation by natural selection. These include, to name a few: random fixation even of antiadaptive traits because of limitations of population size and the colonization of new areas by small numbers of founders; the acquisition of traits because the genes influencing them are dragged along on the same chromosome as some totally unrelated gene that is being selected; and developmental side effects of genes that have been selected for some quite different reason.

An example of the last is the redness of our blood. Presumably we have hemoglobin because natural selection favored the acquisition of a molecule that would carry oxygen from our lungs to the rest of our body, and carbon dioxide along the reverse route. That our blood is red, as opposed to, say, green, is an accidental epiphenomenon of hemoglobin’s molecular structure, and a few animals, like lobsters, have green blood. This has not stopped adaptationist ideologues from inventing stories about why blood ought to be red, but they are not taken seriously by most biologists.

Despite the fact that mechanisms of nonadaptive evolution are firmly entrenched as part of modern evolutionary explanation and are discussed at some length in Futuyma’s book, they are dismissed by Ruse as only “background noise against the main evolutionary tune.” It may be, however, that Professor Ruse’s ear is not accustomed to counterpoint.

A more realistic and less ideological view of the current problems and controversies in evolutionary theory can be seen in Evolution Now, although the lay reader will find it hard going. It includes chapters on the evolution of the structure of genes themselves and how they are grouped together on the chromosome partly as a consequence of adaptive forces and partly as a trace of purely historical accident. One section concerns the speed of evolution, and whether most evolutionary change may occur during short periods at the time that new species are formed. An ultra-adaptationist section deals with the evolution of behavior and an antiadaptationist section with parasitic DNA. Most of the ideas in this book will turn out to be false alarms, but they illustrate the richness of evolutionary phenomenology as opposed to the poverty of a mindless adaptationist program.

  1. 7

    Darwin, The Origin of Species, introduction.

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