A Good Tautology is Hard to Avoid

 

Critics of evolutionary theory have long argued that the concept of natural selection is a tautology.  John Wilkins seeks to counter this argument in his article “A Good Tautology is Hard to Find” on the site, The Talk.Origins Archive.

 

Wilkins’ discussion, found at http://www.talkorigins.org/faqs/evolphil/tautology.html, contains two points that I would like to address.  The first is Wilkins’ contention that the concept of natural selection is not a tautology.  The second is his contention that natural selection rules out many possibilities, which adds to its substantive explanatory power.  Let’s examine each of these points in turn.

 

Tautology

 

In his article, Wilkins states:

 

“The simple version of the so-called ‘tautology argument’ is this: Natural selection is the survival of the fittest. The fittest are those that survive.  Therefore, evolution by natural selection is a tautology (a circular definition).

 

The real significance of this argument is not the argument itself, but that it was taken seriously by any professional philosophers at all.  ‘Fitness’ to Darwin meant not those that survive, but those that could be expected to survive because of their adaptations and functional efficiency, when compared to others in the population.”

 

In other words, according to Wilkins, Darwin used fitness to mean not those that did survive but those that were expected to survive.  Thus Wilkins implies that we will not have a tautology if we reword the definition as follows: “Natural selection is survival of the fittest.  The fittest are those that are expected to survive.”  If natural selection is properly doing its job of selecting, which we are assured it always does, then those that are expected to survive will be those that will survive.  So if we take what would otherwise be a tautology and change the verb tense, then it is no longer a tautology?

 

The problem is that under Wilkins’ approach, natural selection will mean nothing more than survival of those that are expected to survive, and we are still left with a tautology.  We haven’t gotten anywhere by shifting the focus from those that did survive to those that are expected to survive.  In fairness, there is a way out of the tautology problem, as I will discuss below, but natural selection needs to be formulated much more carefully than just proposing that we should focus on expected survival rather than actual survival.

 

Wilkins’ next sentence is as follows:

 

“This is not a tautology, or, if it is, then so is the Newtonian equation F=ma (Sober 1984, chapter 2), which is the basis for a lot of ordinary physical explanation.”

 

This is tantamount to saying: “Even if natural selection is a tautology, so what?  It still explains lots of good stuff.”  Now I doubt Wilkins really believes that F=ma is a tautology; rather he is arguing that the logical construction of natural selection is essentially analogous to other constructions that we accept as good, valid scientific statements.  Unfortunately, there is too much reliance on Sober and too much reliance on a bad analogy.

 

Wilkins’ confusion results from a failure to distinguish between two very different logical constructions: equivalence and tautology.  Equivalence is a pure A=B construction.  Under Wilkins’ statement, 6=2*3 would also be a tautology.  But it is not; it is a statement of equivalence.

 

In contrast, a tautology is essentially a logical argument or proposition of causation (or, if you prefer, premise and conclusion) with two parts: (1) an if . . . then . . . relationship, such as If A, then B, coupled with (2) a definition of A (the cause or the premise) by reference to B (the effect or the conclusion).  This is precisely the problem that plagues natural selection as it is so often described: If the organism is fit, then it will survive; and fitness means that it did survive (or will survive, or is expected to survive, take your pick).

 

Let’s look again at the Newtonian equation F=ma.  Even though force, mass and acceleration can be mathematically described in terms of each other, they do not cause each other.  Force doesn’t cause mass; mass doesn’t cause acceleration.  The mathematical equation is an equivalence statement of their relationship.

 

In contrast, natural selection posits a cause-effect relationship.  Because of an organism’s fitness, it is theorized, the organism survived (will survive, is expected to survive, etc.).  Thus natural selection is in the business of explaining what leads to or causes survival.  So far, so good.  But when we then seek to explain this causal relationship by defining the causative element (“fitness”) in terms of the resulting element (“survival”), we have a tautology.

 

I indicated that there is a way out of the tautology problem, and there is.  But only if the cause, fitness, is carefully defined by reference to characteristics that are independent of the result, survival.  Thus, natural selection would not be a tautology if we define fitness in terms of independent characteristics such as speed, or bodily efficiency, or reproductive capability.  If we define fitness this way, then we can hypothesize that natural selection actually means survival of the fleetest, or survival of the most efficient, or survival of the most prolific.

 

Later in his article Wilkins alludes to such possible approaches to an understanding of fitness.  This is certainly a step in the right direction, and if a careful definition of fitness is adopted we can avoid the tautology fallacy.  However, the recurring frustration voiced by critics of evolutionary theory is that proposed definitions are notoriously slippery, and it seems nearly impossible to pin evolutionary theorists down on a working definition.  And without a concrete working definition of the causative element, what exactly is it that we are supposed to test?

 

This is the kind of frustration with the concept of natural selection voiced by many critics, and that brings us to Wilkins’ second point.

 

Ruling Out

 

Wilkins states:

 

“However, there is another, more sophisticated version [of the tautology argument], due mainly to Karl Popper (1976: sect. 37).  According to Popper, any situation where species exist is compatible with Darwinian explanation, because if those species were not adapted, they would not exist.  That is, Popper says, we define adaptation as that which is sufficient for existence in a given environment.  Therefore, since nothing is ruled out, the theory has no explanatory power, for everything is ruled in.

 

This is not true, as a number of critics of Popper have observed since (eg, Stamos (1996) (note 1)).  Darwinian theory rules out quite a lot.  It rules out the existence of inefficient organisms when more efficient organisms are about.  It rules out change that is theoretically impossible (according to the laws of genetics, ontogeny, and molecular biology) to achieve in gradual and adaptive steps (see Dawkins (1996)).  It rules out new species being established without ancestral species.”

 

What Wilkins is saying in effect is that because genetics, ontogeny, molecular biology, etc. are testable hypotheses, and because natural selection is presumed not to violate them, then natural selection rules out violations of those natural laws, which adds to its explanatory power.

 

First of all, Popper was no doubt making a practical point about the substantial challenge of pinning down a working definition of the causative element, and thus the practical difficulty of natural selection teaching us anything useful.  No doubt Popper would agree that violations of natural law are not available to natural selection.

 

Second, with apologies to Dawkins, whom Wilkins cites, I believe a moment’s reflection will tell us that natural selection does not rule out violations of genetics; genetics does.  It does not rule out violations of molecular biology; molecular biology does.

 

To be sure, natural selection’s inability to violate well-established natural laws is a welcome admission, but Wilkins implies that this is a property of natural selection itself.  This is like saying that archeology rules out violations of physics.  No it doesn’t; physics does.  Natural selection cannot set the parameters of genetics or molecular biology or physics; it can only be bound by them.  Ultimately, Wilkins’ statement is probably an example of attributing much more explanatory power to natural selection than it really has.

 

True enough for natural laws you say, but what about the first “ruling out” cited by Wilkins in the above quote: namely, that natural selection “rules out the existence of inefficient organisms when more efficient organisms are about?”  Now we are getting somewhere.  I believe this “ruling out” is in fact a logically appropriate statement.  Now if only we could come up with a concrete definition of efficiency, then we would have a definition of fitness that we could apply and test.

 

Unfortunately, despite all the intervening decades since Darwin, we still seem to be unable to come to any concrete working definition of fitness.  This is the source of the disillusionment with the concept of natural selection expressed by so many.

 

Conclusion

 

The concept of natural selection as proposed by Darwin, and as often applied today, is likely a tautology.  The only way for us to keep it from failing as a tautology is to carefully define fitness in terms of characteristics that are independent of survivability.  And once saved from this logical precipice, the only way to give natural selection any real explanatory substance is to come up with a concrete working definition of fitness that can be tested.  Although various vague characteristics have been proposed, such as efficiency, it has been notoriously difficult to pin down any useful working definition of fitness over the past century and a half.  Without such a definition, we cannot carry out meaningful empirical test to determine the correctness of the hypothesis.

 

Given the difficulties of defining fitness in a meaningful way, a word play on the title of Wilkins’ article might provide us with an appropriate motto for evolutionary theory today: “A Good Tautology is Hard to Avoid.”

 

 

Eric Anderson

July 18, 2003

 

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