A recent discussion about Ohm's Law led me to think a bit more deeply about the character of physical law. My mech. eng. friends may recall a few occasions when I pointed out that Newton's second law, F=ma, is merely a definition of what force is; likewise, I am inclined to point out to at least one electrical engineer who reads this blog that resistance is merely defined via Ohm's law. Before anyone starts accusing me of undermining the foundations of their profession, let me first state that I am a physicist, and these issues trouble me greatly -- if the Second Law is tautologically true by definition, then have we really been talking in circles for the last 300 years? But I am already digressing, because I actually want to discuss... "survival of the fittest".
First, the wikipedia article explaining the tautology problem:
- "Survival of the fittest" is sometimes claimed to be a tautology. The reasoning is that if one takes the term "fit" to mean "endowed with phenotypic characteristics which improve chances of survival and reproduction" (which is roughly how Spencer understood it), then "survival of the fittest" can simply be rewritten as "survival of those who are better equipped for surviving". Furthermore, the expression does become a tautology if one uses the most widely accepted definition of "fitness" in modern biology, namely reproductive success itself (rather than any set of characters conducive to this reproductive success). This reasoning is sometimes used to claim that Darwin's entire theory of evolution by natural selection is fundamentally tautological, and therefore devoid of any explanatory power.
Now, the evolutionists will go up in arms at this blasphemy. "How dare anyone contest the views of the great prophet Darwin? He must be from the Creationist side!" There are a lot of heated online discussions on this issue, and they are mostly quite amusing. The defence of Darwin usually goes something like this: "...survival of the fittest is not tautological because it is falsifiable... there are instances where the fittest do not survive...", or, "fittest is not merely defined as being better equipped for survival and reproduction...there are criteria for fitness that are independent of survival..." Now, these arguments look to me like they are desperately trying to salvage the phrase in question from tautological status. There are even arguments like "...every scientific law can be phrased as a tautology: Newton's law of gravitation can be rephrased as 'the ball is falling, therefore it falls'. Relativity can be phrased as 'light bends in a gravitational field, therefore, if I shine light into a gravitational field, it bends'..." There is of course, creative name-calling and insult hurling between intellectuals as well...
One type of tautology is a statement that has the form "if A, then A". For instance, "light bends in a gravitational field, therefore, if I shine light into a gravitational field, it bends" is such a tautology. However, it certainly does not follow that "A", the physical law under scrutiny, is tautological. One the other hand, if you define "fittest" as "best survivability/reproductivity", then "survival of the fittest" takes on the form "A=>A(<=>B)" which is tautological and also the content of the phrase itself. A possible escape route is to do a sneaky redefinition of "fittest". Under this new definition, one can accomodate "fit" creatures that wind up dead (these were not considered fit under the original definition), providing the desired counterexample. But this approach compromises the universal validity of "survival of the fittest", and besides, should one be satisfied with this sleight-of-hand? Putting it in another way, does the omniscient God Himself not know the set of factors that determine the likelihood of survival of any particular species? Does such an exhaustive list not exist in principle, albeit hidden from our finite-sized brains? Is the proposed redefinition, then, an admission of our ignorance rather than a logical necessity?
But, one protests, "Bull-crap! How can the concept of 'survival of the fittest' be tautological when it has so evidently taught us so much?" Contrary to what a defensive Darwinist might think, the tautological status of "survival of the fittest" does not render the entire theory of evolution meaningless. Let me elaborate on my point of view. Use of the word "fittest" implicitly suggests that one can compare, quantitatively, the survivability of a species versus another. Mathematically speaking, this means that there exists a map from the set of parameters describing the species and the environment in question to an ordered (or even partially ordered) set. That is, we can, provided we think hard enough, attribute (say) a number to each species, compare the numbers for the species under consideration, and then decide which of these is the fittest. In my opinion, this is the essence of Darwin's evolution -- that there actually exists a well-defined concept of fitness/survivability/whatever-you-wish-to-call-it that allows us, mere mortals, to meaningfully predict what we observe to be natural selection. Combined with the postulate of heredity, one then has a mechanism to explain the phenomenon of evolution. The existence of such a function is not a priori clear, which is why we have a theory of evolution. Indeed, the theory is falsifiable; there simply may not be such a function, for example, if there really is a Creator. The job of the scientist is then to search for the functional dependence of fitness/survivability on the parameters at hand, or at least, to suggest a plausible simplified approximation for such a function. And then we can start talking... :)
So, do not worry! The theory of evolution is still a legitimate and rich one, despite "survival of the fittest" being a tautology. Therefore, we should not hope to get "free" explanatory power from this popularized catch-phrase (e.g. the dinosaurs died out because the mammals were fitter than them / humans dominate the planet today because we are the fittest, etc.), but should instead seek a comprehensive characterization of fitness, and look actively for possible improvements in the details of the theory. Tautologies are commonplace in a good theory (a proof can be argued to be a convoluted tautology), but the real danger is using a tautological argument to explain something, or worse still, to justify certain positions (think social Darwinism).
By the way, I also think that F=ma suffers from the same problem, in that it is quite unsatisfactory to say that "the ball is accelerating because there is a force acting on it". But that is another story for another time, and suffice to say, classical mechanics does not reductio ad vacuo (bad grammar) even if you treat F=ma as a definition.
*I have no formal training in the theory of evolution beyond a secondary school level, and only a basic understanding of formal logic. But I understand that professional biologists and logicians do not necessarily speak in the same language.
