Is Natural Selection a Tautology?
July 5, 2006
As I write this, Ann Coulter’s new book Godless: The Church of Liberalism is currently number one on the New York Times’ bestseller list. The book contains four chapters dealing with evolution. In these chapters Coulter, well known for her right-wing polemics, attempts to portray evolution as nothing more than a sham science that serves as a creation myth for political liberals. Reading this material is a curious experience for anyone who knows some freshman biology. As with all anti-evolution writing, the arguments that are presented are not only incorrect, but also so confused that it is frequently difficult to discern what point Coulter thinks she is making.
The present essay will be devoted to just one of the arguments upon which Coulter bases her case. The motivation for this series of essays has always been a desire to use insipid creationist prattle as a tool for promoting clear thinking about basic biological questions. It is hoped that by thinking carefully about why Coulter’s caricature of evolutionary biology is wrong, one can come to better understand the real thing.
The argument in question is sometimes referred to simply as “The Tautology Objection.” Coulter’s version goes like this:
The second prong of Darwin’s “theory” is generally nothing but a circular statement: Through the process of natural selection, the “fittest” survive. Who are the “fittest”? The ones who survive! Why look — it happens every time! The “survival of the fittest” would be a joke if it weren’t part of the belief system of a fanatical cult infesting the Scientific Community.
The beauty of having a scientific theory that’s a tautology is that it can’t be disproved. Evolution cultists denounce “Creation Science” on the grounds that it’s not “science” because it can’t be observed or empirically tested in a laboratory. Guess what else can’t be observed or empirically tested? Evolution! (pp. 212-213).
Writing in National Review Online in December of last year, conservative commentator Tom Bethell expressed the main point more clearly:
Darwin’s claim to fame was his discovery of a mechanism of evolution; he accepted “survival of the fittest” as a good summary of his natural-selection theory. But which ones are the fittest? The ones that survive. There is no criterion of fitness that is independent of survival. Whatever happens, it is the “fittest” that survive — by definition. (Emphasis Added)
Even before considering the minutiae of how fitness is defined, we should note something suspicious about this argument. Coulter and Bethell are not saying here that recent discoveries have shown that evolution is an inadequate theory. Rather, they accuse scientists of having made a simple logical oversight. Paleontologist Stephen Jay Gould observed (in response to a previous article, in Harper’s Magazine, in which Bethell raised the same issue):
Bethell’s argument has a curious ring for most practicing scientists. We are always ready to watch a theory fall under the impact of new data, but we do not expect a great and influential theory to collapse from a logical error in its formulation.
Indeed. Scientists are fully capable of jumping to conclusions, or arriving at incorrect theories from an inadequate supply of data. But it has never once happened in the history of science that a theory achieves mainstream status, only to fall apart when a clever outsider notices a simple logical oversight. That Coulter’s and Bethell’s formulation of evolution suggests it is tautological proves only that they do not understand the theory they are attacking (or are deliberately misrepresenting it, but we will leave aside that possibility for now).
Let us begin our reply to this argument in the most direct way possible. It is asserted that within evolutionary theory, the fittest organisms are defined as those who survive. This is the crux of the argument, and it is completely incorrect. In reality, the fittest organisms are the ones who, based on their physical characteristics and the environment in which they find themselves, would be expected to leave the most offspring. Gould described the point this way:
My defense of Darwin is neither startling, novel, nor profound. I merely assert that Darwin was justified in analogizing natural selection with animal breeding. In artificial selection, a breeder’s desire represents a “change of environment” for a population. In this new environment, certain traits are superior a priori; (they surive and spread by our breeder’s choice, but this is a result of their fitness, not a definition of it). In nature, Darwinian evolution is also a response to changing environments. Now, the key point: certain morphological, physiological and behvioral traits should be superior a priori as designs for living in new environments. These traits confer fitness by an engineer’s criterion of good design, not by the empirical fact of their survival and spread. It got colder before the wooly mammoth evolved its shaggy coat.
Let us imagine that we have perfect information about the environment in which a population of organisms finds itself. Let us further suppose that we are aware of the full range of extant heritable variation within the population. In those circumstances we could make some definite statements about the future evolution of that population. A group of scientists could examine that information and come to a consensus about which members of the population were the fittest. Plainly there are criteria for fitness independent of mere survival.
This is not the whole story, however. Predicting the future is only a very small part of what evolutionary biology is all about. Most of the interesting events in evolution took place in the distant past. Unraveling and explaining that past presents scientists with a problem almost perfectly opposite to the one considered in the previous paragraph. Instead of trying to predict the future evolution of a species given information about its present environment, now we are trying to understand ancestral environments given information about what sorts of creatures survived.
In this context scientists will, indeed, hypothesize that traits that persisted and developed over long periods of time did so because of the fitness advantages they conferred on their possessors. But here’s the catch: that’s the beginning, not the end, of the investigation. The assumption that the trait under investigation emerged from the prolonged result of natural selection is used to generate testable hypotheses about the creatures in question. In his book Plan and Purpose in Nature, biologist George C. Williams provides the following example:
Productive use of the idea of functional design, in modern biological research, often takes this form: an organism is observed to have a certain feature, and the observer wonders what good it might be. For instance, dissection and examination of a pony fish shows it to have what looks like a light-producing organ, or photopore, and even a reflector behind it to make it shine in a specific direction. So we accept the conclusion that the organ is good at producing light, but the obvious question then becomes, What good is light? The pony fish photopore is deep inside the body. Can it really be adaptive for a fish to illuminate its own innards?
The organ is situated above the air bladder, and the light shines downward through the viscera. The pony fish is small and its tissues are rather transparent. Some of the light gets through and produces a faint glow along the ventral surface. But what is the use of a dimly lit belly? Perhaps it makes the pony fish more difficult to see in the special circumstances in which it lives. It inhabits the open ocean, where it may move toward the surface as darkness approaches, but spends the daylight hours far below at depths where the light is exceedingly dim by our standards, detectable only as a murky glow from above.
Williams goes on to describe how this hypothesis led to experiments that confirmed that the pony fish’s glow has the intensity it ought to have if its primary function was to provide camouflage. This is a nice illustration of how selection-based reasoning is used in scientific practice.
Natural selection is not used as an abstract principle in biological research. “Survival of the fittest” is a catchy phrase that captures much of what is important about natural selection, but it is not one you will find very often in professional research papers. Instead, scientists will propose specific hypotheses about the fitness advantages conferred by particular traits in particular environments. There is nothing tautological about saying, for example, that moths possessing dark coloration will be less visible than light colored moths to predatory birds when resting on dark-colored trees.
The reasoning used by scientists in this way is comparable to what historians do in trying to understand why certain events happened the way they did. An historian studying nineteenth century America might begin his investigation with the fact that the North won the Civil War. From this starting point he will naturally ask himself what advantages the North had that allowed them to emerge victorious over the South. But the assumption that the North had such advantages will not be the sum total of his investigation. And no one would consider it reasonable to object to his work on the grounds that it is based on circular reasoning.
Well, populations of organisms that survive through long stretches of evolutionary history are likewise the victors in a war, this time for survival. It is perfectly reasonable to assume that those that survived had certain advantages over those that did not. Determining the precise nature of those advantages might pose a difficult practical problem, but the assertion that those advantages existed is surely unproblematic.
We have thus provided two answers to the tautology objection. The first is that its central premise, that there are no criteria of fitness independent of survival, is false. The second is that natural selection is not applied in practice in the simplistic way the phrase “Survival of the fittest,” suggests. Instead, scientists use selection based reasoning to develop specific, testable hypotheses about the organisms under investigation.
Stephen Jay Gould once observed that creationists are “singularly devoid of shame” in their willingness to use any argument, no matter how vacuous or frequently refuted, in making their case against evolution. He might have included right-wing demagogues alongside creationists. The tautology objection cannot survive the scrutiny of anyone versed in even the most basic elements of evolutionary theory. That Coulter would raise the issue so snidely, and have her book sell very well as a result, proves that knowing what you are talking about has no value for many on the political right.