One of the most common arguments against evolution put forward by creationist laypeople goes something like this: "Either evolution is true or creationism is. If evolution is true, then we all got here by random chance. I just can't believe that; there's too much order, complexity and beauty in this world for it all to be the result of chance. Therefore, creationism must be true."

Aside from the false dilemma that arises from assuming evolutionary theory and Judeo-Christian creationism are the only two options, there is a more fundamental error in this argument, one that cuts to the heart of the evolution/creationism debate. Creationists often say they find it inconceivable that pure chance could have produced all the complexity and diversity of life. And evolutionary scientists agree, because evolution says nothing of the kind. This is a crucial fact that must be grasped by anyone hoping to speak on this issue knowledgeably: Evolution is not chance.

To conceive of evolution as nothing more than blind chance and randomness is the most serious conceptual mistake one can make. Evolution does contain a component of chance, but there is far more to the process than that, and it is precisely the existence of the non-chance components that allows evolution to work. The process of evolution is driven by the engine of natural selection, a filter that extracts order out of chaos according to a fixed and non-random set of rules. It is for this reason that many of the most common creationist caricatures of evolution fail. Evolution is not like an explosion in a print shop producing a dictionary, a tornado in a junkyard producing a 747, or DNA in a blender producing a human being, because all of these lack a component of non-random selection.

Described in its simplest terms, evolution is easy to understand. Due to mutation, organisms undergo random changes, some of which are beneficial, while others are not. The organisms with beneficial changes enjoy a competitive advantage, and these changes are passed on throughout the population and become common; those with deleterious changes are at a disadvantage, are less likely to reproduce, and do not pass these changes on, causing them to disappear out of the population. This is natural selection in a nutshell. Within the scientific community, there are debates about topics such as the level at which selection operates or the relative rate of evolutionary change, but the simple principles outlined above lie at the heart of all versions of evolutionary theory.

It is clear to see that natural selection, which is not chance but the opposite of chance, is what makes evolution work. If there were no selection, change in living things would follow a pattern called a "random walk" - sometimes the changes would be beneficial, sometimes not, and the population as a whole would wander back and forth across the fitness "landscape" but, on average, never get anywhere. That would be an example of random change, and it is absolutely correct to say that such a process could never produce all the intricate diversity and marvelous adaptations that living things possess.

Natural selection changes all that, by preferentially preserving the good variations and eliminating the bad ones. It is like a ratchet, allowing a population to move only in one direction - the direction of greater fitness. And the changes that natural selection favors are not random, but are determined by the characteristics of the environment. This is why, for example, both fish and aquatic mammals such as whales and dolphins have the same streamlined body shape - because this is the shape that is most efficient for moving through the water in which they live. This shape has evolved separately in the fish and cetacean lineages, in an example of an evolutionary phenomenon called convergence, precisely because it is the best shape for that environment regardless of what kind of creature has it. If evolution were random, we would not see this kind of predictable pattern.

Like all natural processes, evolution is guided by laws that do not change. If you throw a rock up in the air, its path is not governed by pure chance, but by the law of gravity. It cannot fly off randomly in any direction, but will travel in a parabolic arc and land at a predictable point. If you put a hot object next to a cold one, the transfer of heat is not governed by pure chance, but by the laws of thermodynamics. Heat cannot flow randomly in either direction; it will move consistently from the hotter object to the colder one. And if you set a population of randomly mutating organisms in an environment, their future is not drifting at the whim of chance, but is directed by the law of natural selection. Their evolution will not proceed in just any direction, but only in those that make them better adapted to their surroundings.

Granted, the mutations that provide the raw material for selection to operate on are random, in the sense that they are not predisposed to increase fitness. Beneficial mutations are not preferentially more likely than deleterious ones, and organisms do not "know" how they "need" to mutate in order to survive. It is merely that the ones that do mutate in helpful ways survive better and reproduce more abundantly than those that do not.

This has led to creationists charging that evolution is random in another sense, that it did not require humans to evolve; that is, there is no inevitability to it. And as far as science can determine, this is an accurate statement. Although we can confidently predict that there will be mutations that increase fitness, we cannot predict exactly what mutations they will be or what form they will take. The evolution of Homo sapiens was the result of a long chain of contingencies, and if any event in our evolutionary past had turned out slightly differently, we might exist in a dramatically altered way, or we might not exist at all. There is no scientific evidence that humans' existence was inevitable or that evolution in general has any predetermined goals.

But these things are true only as far as science can determine. If one's personal convictions are such that God intended for humanity to develop all along and guided the course of evolution appropriately, that is not a belief that science can speak to. (That God was working behind the scenes to guide the course of events, despite a lack of any obvious sign of this, is of course a belief common to many religions.) For this reason, the theory of evolution has nothing to say about whether God exists or whether there was a deeper plan to life, though of course, individual scientists are free to take a position on either side of that issue.

But evolution itself is a science, and like all sciences, it tells us only what is, not what should be. It is a description of one particular aspect of reality, and that is all it is. It would be foolish to use it in an attempt to derive a moral code, a purpose for our lives, a meaning to life, or any such thing. Those things do not fall within the realm of science, and science will not give us answers to them; it is up to us as individuals to decide that for ourselves. Some people seek answers to these questions through religion, while others find them through other paths.

When creationists say that one who accepts evolution must believe that life is nothing but the result of random chance, they are abusing the theory. In the scientific sense, this conclusion leaves out the most important part of the entire theory, and in the metaphysical sense, this is a deceptive attempt to derive from the theory an explanation of something it was never meant to explain. Evolution does not tell us that our life is the purposeless result of chance; it does not say anything on the topic at all. Either way, the creationists' conclusion is flatly inaccurate. Their strategy is to tar evolution with offensive-sounding implications and turn people away from it regardless of the evidence, but this fallacious attack will always wither before the truth.

Recommended Links:

• The Talk.Origins Archive: Evolution and Chance