Biological evolution presumably functions by mutation, genetic drift, migration and natural selection. Natural selection is supposed to operate through differential reproduction or "survival-of-the-fittest." Is "survival-of-the-fittest" a rational basis for the concept of biological evolution? This question can be answered "no" with certainty.
Consider the following two theses:
The principle encompassed by the phrase "survival-of-the-fittest" can be expressed by the biconditional statement "A if and only if B." In such a statement, A and B may be different ways of stating exactly the same idea. If so, the sentence "A if and only if B" is a type of tautology -- it is always true. Conversely, if A and B express different ideas then the statement "A if and only if B" is regarded as false when either A is true and B is false or B is true and A is false.
If the particular sentence with which this chapter is concerned is viewed as a tautology, then it is just as devoid of scientific content as the sentence "a man is married if and only if the man is a husband." If A and B express different ideas, then circumstances must be found such that the truth of A and the truth of B can be independently tested before the truth of the biconditional can be evaluated. Herein lies the problem. The truth of "creature is most fit" cannot be tested for any creature under any circumstances because the overall "fitness" of the creature can neither be measured nor computed. Since the truth of A is untestable, it follows that the truth of "A if and only if B" is likewise untestable. Therefore, the answer to the question addressed in this chapter is "no."
Although deficiencies fatal to the theory of biochemical evolution are gradually being recognized by the scientific community, our inability to measure or compute the "fitness" of a creature has not yet been viewed as fatal to the theory of biological evolution. Investigators generally settle for measuring small numbers of morphological, physiological or behavioral "traits" and insinuate that, if all other aspects of "fitness" are fixed, these traits alone will suffice. Unfortunately, no theory is available which shows how the vast majority of aspects may be fixed while a chosen few are free to vary. A change in a single trait may alter 1000 aspects important to the overall "fitness" of an organism. What sort of interfering parameters might exist cannot even be imagined due to the absence of a theory for reducing the organism to a calculable whole.
If the concept of natural selection is clearly untestable, why does the theory of biological evolution continue to dominate the field of biology? Partly because the concept's untestability makes it immune to falsification. Partly because the concept has become integrated into the common working knowledge of the biological community and has become the context within which that community understands the world. Partly because the alternative appears to involve God. (10)