Evolution is Not a Tautology

Evolution Is Not a Tautology

Strong words from the last angry man
by Alan Moses

Consider the following description of the processes of evolution from a first-year philosophy course: “Fitness is defined as the ability of an organism to interact with its environment in order to survive and produce as many offspring as possible. Natural selection is defined as the process by which the less fit are weeded out in time because of their inability to reproduce. Populations become more and more fit because they are composed of individuals that have managed to out-compete the less fit.” But wait a minute—of course the fitter creatures have out-competed the others; that’s how we defined fitness. Doesn’t that make Darwin’s theory of evolution by natural selection circular, equivalent to explaining that my uncle is a bachelor because he’s an unmarried man? You can’t explain why some animals survive by saying they were more fit, since fitness is defined as the ability to survive.

Admittedly, this kind of argument is tempting— imagine breaking the cornerstone of modern biology by simply pointing out a logical flaw. Strangely enough, when you ask philosophy professors how scientists can believe the theory of evolution (and still get grant money) even though it’s so obviously a circular argument, you’ll never get a straight answer. A classic bad response might be: “Well, actually, all scientific theories are tautologies; look at ‘F = ma’. Force (F) is defined in terms of mass (m) and acceleration (a), while mass is defined as force divided by acceleration. It’s totally circular.” My purpose here is not (as it might seem) to slander my college education or my philosophy professor. It is to give a better answer about the question of evolution, a subject plagued not only by bad arguments, but also by bad responses to those arguments.

It turns out that the philosophy-class description of evolution given above leaves out two crucial aspects of the theory. The first is obvious: fitter organisms survive because they actually are more fit, not because they were defined as fit after the fact. Said another way, my uncle is a bachelor because he has certain qualities that prevent him from getting married: he has big ears, he burps in public and he eats incredible amounts of canned sardines. Fitter animals survive and reproduce because they run faster, jump higher or sing more beautifully than their peers—not because we called them more fit. Notice how difficult it can be to define fitness. My bachelor uncle’s fitness depends greatly on whether sardines are in style or big ears are desirable. Sometimes, particularly in the case of extinct species known only through fossil remains, we may never be able to say what led them to evolve a particular combination of features. These unknowable details of biological history are called “just so stories” by evolutionists.

The second premise of Darwin’s theory of evolution is something we all take for granted, but which turns out to be crucial empirical evidence for the mechanism of natural selection. Simply put, children are like their parents. The apple doesn’t far fall from the tree; kids are chips off the old block. A more rigorous way to phrase this might be that traits (good and bad) are transmitted from one generation to the next. Until fifty years ago, this was only an empirical rule; today, the genetic mechanism by which traits are transmitted is understood in molecular detail. Without this crucial step, evolution through natural selection makes no sense at all. It’s important to note that a corollary is also true: apples don’t fall far from the tree, but they don’t fall too closely either— if children were exactly like their parents, evolution would be impossible.

So, evolution by natural selection has two hidden assumptions. First, it is assumed that there is a “just so story” about why and how a particular feature was useful to a particular creature at a particular time. Second, it is assumed that these features can be passed from generation to generation. Both of these assumptions were simply taken for granted before Darwin—it was obvious to everyone that each animal had the features it needed to do what it was doing, i.e. the features that made it fit. And everyone just needed to take one look at their uncles to know that family members resembled each other.

What is striking about Darwin’s theory is that once you accept those two assumptions (which, in Darwin’s time, everyone already did) natural selection must logically follow. If members of a set produce members that are similar to themselves, then, in time, the set will grow to be composed of members who have inherited the characteristics that allowed them to be produced. This statement is not true by definition. It is an abstract truth of logic, given a few biological assumptions. Nevertheless, we should realize that, as is the case with any empirical rule, there are exceptions where these assumptions fail—and as soon as they do, so will Darwin’s venerated mechanism.