Topics Biology

Question I'm passionately interested in Darwin and evolution, but have been bashing my head against the wall recently, over the objection that 'survival of the fittest' is a tautology. The answers to this that I've read state that 'fitness' doesn't mean: "those that survive, but those that could be expected to survive because of their adaptations and functional efficiency" [http://www.talkorigins.org/faqs/evolphil/tautology.html]. But then the reply to this seems to be: "This charge is not repelled by substituting "most adaptable" or "best designed," etc., for "fittest," because these too are determined by survival. (That is, how do we determine that a species, or members of a species, is "most adaptable" or "best designed"? By the fact that it survived.)" [http://members.iinet.net.au/~sejones/PoE/pe02phl3.html] As an aside following on from this, I know that you can then say that there is a lot of evidence. But isn't this evidence for evolution, not the specific theory of natural selection? My question is: is there a logical rebuttal to the statement that it is a tautology, and therefore apparently 'devoid of explanatory power'? I'm actually rather worried about this, having based much of how I view the world on natural selection. Thanks, and sorry if the answer is very obvious to you!

Accepted:
February 13, 2009

Comments

My understanding of the supposed tautology to which you refer isthis:

In the theory of evolution, only the most fit organisms survive.
But the fitness of an organism can only be determined by the fact that it survived.
So, we conclude: 'In the theory of evolution, only those that survive survive'

The statement in (3) is indeed quitemeaningless. If this were indeed the basis of evolution, then itwould have no predictive power, and fail a key test of beingscientific. Because the primary object that evolution seeks tounderstand is the past through the fossil record (and similarevidence), and it is successful species that leave such traces, it isindeed the case the palaeontologists have to work backwards fromsurvival to fitness.

There are several problems with theabove reasoning, however. First, 'fitness' is not an attribute of anorganism or of its genes. Rather, it is a relation of the heritablecharacteristics of an organism to its environment (including otherorganisms and also things like climate) insofar as this affectslikely reproductive success. That it is relational creates problemsfor science, to be sure, since environments are enormously complex.But it does allow at least statistical predictions to be made, whichcan be tested. So, for example, the the various lists of endangeredspecies are predictions concerns which species have declined infitness. But these predictions are not entirely based uponextrapolations forward of a mere decline in numbers over recentyears. Rather, at least some are based upon an evaluation of thelikely impact of a changed environment (e.g. loss of habitat, climatechange, pollutants, invasive species, etc.) upon an organism'sreproductive prospects. Likewise, the concept of an 'evolutionaryarms race' permits naturalists to predict where examples ofreciprocal adaptation to new environments may have taken place, andthus test their hypotheses. Finally, consider the following: thefossil record indicates a mass-extinction event 65 million years ago;that is, on a global scale the fitness of most then-extant speciesdeclined rapidly. Only some world-wide change in the environmentcould account for this. This led scientists to hypothesise that anasteroid impact had been responsible. So, research projects wereembarked upon to provide evidence for or against this hypothesis.Globally increased concentrations of iridium at the boundary layerand an impact crater of the correct size and date in Yucatan werediscovered. Although still controversial, this impact theory is adramatic example of the predictive power of the concept of fitness.

Second, survival of the fittest is byno means a complete picture. We also need to add in the idea ofadaptation. By adaptation is meant that, by some process (e.g.mutation), new heritable traits emerge which increase or decreasefitness. This gives the whole account extra explanatory power,because it allows the fossil record to be organised according to thegradual descent of species. Likewise, it makes predictions, such aswhere in the descent 'missing links' are likely to be found (andoften are) by future fossil hunters.

The above observations seem to show in various ways that 'fitness' does not simply mean 'did in fact survive', but rather carries both explanatory and predictive power, which is what the original objection hoped to discredit.