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The Confusion over Evolution

The Ant and the Peacock: Altruism and Sexual Selection from Darwin to Today

by Helena Cronin
Cambridge University Press, 490 pp., $39.50

On Methuselah’s Trail: Living Fossils and the Great Extinctions

by Peter Douglas Ward
W. H. Freeman, 212 pp., $18.95

Oliver Cromwell delivered history’s most famous rebuke to the hero-worshiping that irons all subtlety into flawless cardboard:

Mr. Lely, I desire you would use all your skill to paint my picture truly like me, and not flatter me at all; but remark all these roughnesses, pimples, warts, and everything as you see me, otherwise I will never pay a farthing for it.

Helena Cronin, in The Ant and the Peacock, displays a raw talent clearly equal to that of our finest portraitists, but has placed herself into a position even worse than Mr. Lely’s. Cromwell’s painter at least faced the subject himself; Cronin has produced an uncritical gloss upon a false and simplistic view that never was more than a caricature of Darwinian theory.

As its most deliciously radical component, Darwin’s original theory proposed a causal mechanism for evolution by natural selection among organisms struggling for personal reproductive success—and nothing else. Consider the impact of this cleansing upon the older tradition of natural theology—the creationist principle that sought to prove not only God’s existence, but also his attributes of power and goodness, from the excellent design of organisms and the intrinsic harmony of ecosystems. Darwin acknowledged these aspects of nature, but labeled them as sequelae, or side consequences, of the only causal force operating in evolutionary change: organisms struggling for themselves alone. Quite a contrast: up from below in the “selfish” interest of organisms vs. down from above as directly imposed by a wise creator.

Inevitably, I suppose, Darwin’s success in pulling down the level of causality from an overarching God to a struggle among organisms led some evolutionists to explore a kind of ultimate reductionism in viewing genes themselves as the struggling units, and organisms as mere vehicles constructed for their machinations. Under such a view, called “gene selectionism,” nature’s truly causal competition takes place among different forms of a gene, each “struggling” to leave more copies of its own version in future generations of a population. In classical Darwinism, organisms struggle for reproductive success. (If, for example, short plants are favored by natural selection, then the runts in Mendel’s pea patch produce more surviving offspring, per individual and on average, than the tall plants.) In gene selectionism, the plants are passive vehicles and the struggle occurs among genes. (If you can dredge up your high school biology, you will remember that T and t [“big t” and “little t” even in biological jargon] are different forms [called alleles] of a gene at a chromosomal position [called a locus] influencing the height of the resulting pea plants. Under gene selectionism, little t is struggling with big t to leave more copies of itself in the next generation. Selection is then viewed as working for little t alleles, not for short plants.)

Several of my colleagues toyed with this formulation during the 1970s, while Richard Dawkins provided a popular version in his book The Selfish Gene (1976). This hyper-Darwinian reductionism (and pervasive adaptationism, though from the gene’s point of view) contained some interesting ideas and made a stir within the field. But gene selectionism—as a hard causal claim rather than a colorful metaphor—also received sharp and devastating criticism both from biologists and philosophers.1 Even Richard Dawkins backed away in his next book (The Extended Phenotype, 1982), which opened with the fatal concession that natural selection among genes and ordinary Darwinian selection among organisms may be viewed as equally valid modes of description for the same causal phenomenon. (This stunning admission of relativism flatly contradicted Dawkins’s previous claim for true and exclusive causality at the genic level.)

Helena Cronin, a philosopher by original profession, has gathered much interesting material in The Ant and the Peacock, but her book suffers grievously from the curious and vociferously advocated scheme that she has chosen as her vehicle of presentation. In short, she has somehow received the impression that genic selectionism has accomplished the greatest revolution since Darwin and has swept away all opposition within the field (she proclaims “revolution” as often as Marx or Thomas Kuhn, and labels the new orthodoxy “modern Darwinism”).

Now I freely confess my own strong preference for the other side of this debate—for a model that views selection as operating simultaneously at several levels of a genealogical hierarchy including genes, organisms, local populations, and species. In other words, I argue that no natural entity can properly be described as the exclusive “unit of selection”—as Cronin and Dawkins would claim for genes, and classical Darwinians for organisms. Nature is organized as a hierarchy—genes in organisms, organisms in populations, and populations in species. Entities at each level of the hierarchy can act as biological “individuals,” and Darwin’s process of selection can therefore occur at all levels, with none dominant in all situations. Genes may “struggle” for increased representation in the gene pool of a population, but species may also “struggle” for increased membership of their branches in the “species pool” of an evolutionary lineage.

But whatever one’s personal inclinations, no one can deny the sociological fact that relatively few experts accept the theory of near exclusivity for gene selection, and no amount of blithe verbal assurance about the validity of the theory can convert it into a successful revolution. Most of my colleagues continue to defend Darwin’s view that selection works nearly exclusively on organisms.

For Cronin, ants and peacocks are synecdoches for two great issues mentioned in her subtitle—altruism, epitomized by the behavior of ants in their communities, and sexual selection, the alleged raison d’être of the peacock’s flamboyant and burdensome tail. In Cronin’s view both altruism and sexual selection are explained by the theory of selfish genes; and I agree that the gene’s perspective has been useful in dealing with these two substantial problems. But I shall argue that the peacock only needed classical Darwinism to account for its tail, while the key question evoked by the ant’s altruism has not been resolved. If the approach of gene selectionism is false, then Cronin’s title makes little sense and all her fascinating flowers of insight (primarily on the differences between Darwin and Wallace) languish in barren soil.

This attempt to validate gene selectionism by applying it to ants and peacocks fails for three main reasons (which I consider in turn in the rest of this review): 1) the general theory is bankrupt; 2) the two chosen examples form a false and disparate pairing that either does not need or does not fully illustrate the theory; 3) the theory, even if valid in its own limited realm (which it is not), cannot serve as a paradigm for all, or even much, that evolutionary theory must explain. The fine books of Ward and Eldredge illustrate why this is so.

Fallacy of the General Theory

Since Darwinism is a theory about differential reproductive success (“survival of the fittest” in the old cliché of limited utility), and since organisms are plainly doing the struggling and reproducing “out there” in nature, why would anyone want to relocate the action at the level of genes encased within these organisms? This question engages a central issue in Darwinian theory: On what kind of object does natural selection work? What, in short, is a “unit of selection”? Cronin gives her answer in no uncertain terms:

So when is an “adaptive unit” really an adaptive unit? When is a category that’s seen by us, seen by nature, too? The answer must be: When it’s a unit that selection can work on. For classical Darwinism this would have been difficult to specify precisely. But for modern Darwinism, a unit is obviously a gene and the ramifying tree of all its phenotypic effects [by “phenotypic effects,” she means the manifest characteristics of the organism including its anatomy, etc.].

But if gene selectionism is so self-evidently true, why hasn’t it swept the field, smiting all opposition before it? In a remarkable passage, Cronin admits the stubborn persistence of alternative interpretations, but brands them as obtuse because she so clearly grasps the true logic of genuine Darwinism—and it says what she says it says, period.

Let me forestall the mutterings of disagreement that can already be heard in the background. By no means all modern Darwinians would accept my characterisation. But I am dealing with the theory, not with how individuals have chosen to interpret it. One must distinguish between the fundamental tenets of a theory (what the theory actually says) and how it is viewed by some practitioners (what is said about it). I am dealing with the former.

Cronin’s confidence arises from her misuse of an important distinction between “replicators” and “interactors” made by the philosopher of science David Hull and others. Natural selection is a theory of “differential reproductive success”; therefore, according to one school of thought followed by Cronin, only natural objects that replicate themselves faithfully can be units of selection. For if an object doesn’t replicate itself faithfully, then it cannot be a reliable transmitter of the characteristics that make for superior reproductive success. Now an organism, the traditional “unit of selection” in Darwinism, fails by this criterion because, in sexual reproduction, offspring contain only half the genes of each parent. What good is a replicator that dilutes itself by half in each generation?

The genes themselves, on the other hand, replicate faithfully (except for rare mutation) into future generations. A fecund organism is passing copies of its genes, not its body, into the next generation. Under this view, genes are replicators, while bodies are, in a sense, their servants. Bodies interact with the environment and engage in the “struggle for existence” via differential reproductive success. Bodies are interactors (Richard Dawkins prefers the more loaded and almost pejorative term “vehicles”); genes are replicators. Therefore, only genes are units of selection. Cronin remarks.

Genes, then, can be replicators whereas organisms, groups and other levels of the hierarchy cannot. Natural selection is about the differential survival of replicators. So genes are the only serious candidates for units of selection.

This superficially attractive argument collapses from two major fallacies. First, it is simply not true that only genes replicate with adequate faithfulness. I accept the point that sexual reproduction dilutes the integrity of organisms in replication. But adequate replication returns at higher levels of the hierarchy—populations and species—because splitting at these levels is analogous to asexual reproduction. For example, species split into daughter species that resemble their parental populations far more than any other (descendant dogs are more like ancestral wolves than like any other species). Species are therefore good replicators, and some evolutionary lineages can be more successful than others because their species give rise to more successful branches.

Second, the replicator criterion is at best insufficient, and at worst entirely mistaken. A simple appeal to vernacular usage tells us that a lower unit (a gene, for example) can’t be an exclusive agent if all the action occurs at higher levels (organisms, for example)—and the properties that generate this action are “emergent” characters of the higher level—that is, not a simple summation of features built by the lower units (genes).2 Now, manifestly (and gene selectionists do not deny this), organisms are primary objects struggling for reproductive success in nature. How, then, can “hidden” genes be the true agents if organisms are doing the fighting, cooperating, generating, and dying? Gene selectionists respond that all the relevant properties of organisms can be described as results of the various genes involved in their construction. Such properties, the argument continues, are therefore only the complex manifestation of genetic action.

  1. 1

    See especially E. Sober’s The Nature of Selection (MIT Press, 1984), E. Sober and R. C. Lewontin, “Artifact, Cause and Genic Selection,” Philosophy of Science, Vol. 49, pp. 157–180; E. Lloyd, The Structure and Confirmation of Evolutionary Theory (Greenwood Press, 1988); and P. Godfrey-Smith and R. C. Lewontin’s forthcoming “The Dimensions of Selection,” Philosophy of Science.

  2. 2

    Emergence” is a complex and contentious subject, with a long pedigree, in both the philosophical and biological literature. I use the term here in the narrow technical (virtually statistical) sense. A feature is emergent at any level if its construction requires nonadditive interaction among the factors and components that build it. In other words, if I can make a larger-scale entity D by just adding components A, B, and C together, then nothing about D is emergent—and D can be explained by reduction to its components. But if the building of D requires interactions among A, B, and C that are not inherent in the components considered separately, and cannot be predicted from knowing A, B, and C alone, then D has emergent features and cannot be explained by reduction to its component parts. Organisms clearly have emergent properties, since their features of anatomy, physiology, and behavior are products of complex and nonadditive genetic and environmental interactions—and not the summation of genes considered separately. Therefore, selection operating on organisms cannot be reduced to selection upon genes, and the “gene selectionism” of Cronin’s self-proclaimed “modern Darwinism” fails.

    Incidentally, the concept of emergence helps us to understand why the nature-nurture issue is such a false dichotomy. Genes influence many aspects of human behavior, but we cannot say that such behavior is caused by genes in any direct way. We cannot even claim that a given behavior is, say, 40 percent genetic and 60 percent environmental, and thereby defend at least a partial old-fashioned genetic determinism. Genes and environment interact in a nonadditive way, yielding emergent features in the resulting anatomies, physiologies, and behaviors.

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