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© Copyright 2003, Jim Loy
Darwin's natural selection is one of the mechanisms that drive evolution. Different organisms (plants and animals) are adapted to their environment to greater or lesser degrees. Of those organisms which compete for the same food or space or mates, the better adapted tend to increase in number, while the more poorly adapted tend to die out. If members of the same species are slightly different, those better adapted to the environment will tend to replace those that are less well adapted.
A common (and more or less valid) description of natural selection is "survival of the fittest." The fit survive; the unfit die out. The term "unfit" is not some moral judgement; it just means that these organisms are relatively unfit for their environment. When we look at the results of evolution (change over time), it is usually easy to deduce why one organism died out and another survived. This one is larger; this one had more children; this one is quicker or faster; this one is more intelligent; etc. But if we try to predict beforehand, which organisms will survive, we sometimes come upon unexpected problems.
Let's say that we have two birds of the same species; one is large; one is small. Which one will survive? Obviously the one that is more fit will be more likely to survive. Which one is fit? That's hard to predict. Sometimes larger size is an advantage; at other times it is a disadvantage. The easiest way to tell which bird is fit is to wait and see which one survives. We can state this situation like this:
That list of three "sentences" is circular, and is a tautology. A tautology is a logical statement that is always true, no matter what. An example is "A rose is a rose." Logically, it states a truth so simple that it does not need to be stated. It cannot ever be disproved. And it conveys no logical information; it is logically meaningless. On a subjective philosophical level, it may convey a great deal of meaning, but logically it does not.
If those three sentences were the definition of natural selection, then it would be a tautology. It could never be proved wrong. And it could never predict who will survive or thrive, and who will die out. But those three sentences are not the definition, are they? Those three sentences express this subjective philosophical truth: It is often difficult to know beforehand which organisms are fit and which are not. This does not mean that natural selection does not have predictive power; it only means that it is often difficult to predict. Creationists and even biologists have expressed dissatisfaction with natural selection because of this difficulty. In fact, some biologists have called natural selection a tautology.
But natural selection is not a tautology, because "fit" is much more complicated than those three sentences would suggest. "Fit" means "fit within a certain environment." An environment is difficult to describe. An environment is not just a living space with food. An environment includes other organisms (predators, competing organisms, members of the opposite sex, etc.) and their interactions. This vast web of interactions may be too complicated for scientists or computers to describe, especially with inadequate data. Predictions can be made, often with great success. But there is always uncertainty, probable error of varying amounts, as there always is in science. Biologists would like the uncertainty to be as tiny as it is in physics, but it is not.
Is natural selection a tautology? Well, it can certainly be stated as a tautology, but the tautology is a simplification. The tautology is food for thought. But natural selection is not a tautology.