Creation/Evolution Journal

Biological Evolution and the Second Law

Creationists make much of the second law of thermodynamics. They say it precludes the possibility of evolution because: "There is a general tendency of all observed systems to go from order to disorder, reflecting dissipation of energy available for future transformations—the law of increasing entropy" (Lindsay, 1968). The second law has been stated in many other ways, but we have picked this definition because it contains the all-important word tendency and because it is a definition often quoted by creationists. The word tendency is very critical, since it allows exceptions to the usual implication by creationists that all systems go to disorder. (One can get into many semantic arguments with words like disordered. Technically, an "ordered" state can be described with a minimum of statements or rules. Thus a page of nothing but A's would be more "ordered" than this page of text. We really should use a phrase like high information content in place of ordered, but let's stick with ordered because it's easier to say. Perhaps that's the reason creationists often say ordered when they really mean high information content.)

Consider how different the world would be if all systems became less energetic and less organized with time. There would be no puffy clouds, thunderstorms, or weather fronts. Their organization and energy would have dissipated long ago. There would be no trees or flowers. Their seeds would just decay. And we wouldn't be here either. Each of us would have died as a withering zygote that could not undergo development. Clearly the creationist implication that all systems tend toward decay and disorder is wrong. There are many systems besides evolution that tend toward greater order. Philip Morrison (1978), for example, has shown that spontaneous increases in order are common in our world. He points out that the second law really says that increases in order must be paid for in energy. Such increases are clearly not impossible except in closed systems lacking a source of energy. Where large amounts of energy are available, as in the sun-earth system, large increases in order are possible.

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Creationists, of course, deny this while claiming that organisms contain some sort of God-given precoded plan and energy conversion system that allows them to escape the death and decay dictated by the second law. On the other hand, almost all scientists accept both the second law and evolution. We need to ask, therefore, just how the second law does affect living systems. A look at gene mutation should allow an answer to this question. A given normal gene will mutate to a nonfunctional version of itself with a characteristic frequency, often on the order of 1/1,000,000. (For every 999,999 times this gene is transmitted correctly to the next generation, it is transmitted incorrectly one time.) We could call this type of mutation from functional to nonfunctional a "damaging" mutation.

It comes as a surprise to some people, but nonfunctional genes occasionally mutate back to the functional version. We could call this a "repair" mutation. If genes were likened to cars, this would be like saying that occasionally a dented car could be correctly fixed by being in a second accident! However, genes are not cars; chemical complexity is not the same thing as physical complexity. Even though an explosion in a print shop will not produce a dictionary, energy can change simple methane and ammonia into complex amino acids, as Stanley Miller and Harold Urey demonstrated in 1953. Similarly, even though a second collision probably will not undent a dented car, a second mutational event occasionally renders a gene functional again.

The effect of the second law is clearly seen when the repair mutation rate is measured. This repair rate is always less than the damaging mutation rate. In other words, it is easier to go from an ordered state (functional) to a disordered state (nonfunctional) than it is to go in the reverse direction. A typical rate for this repair type of mutation is on the order of 1/1,000,000,000. This is the most important consequence of the second law on living systems. Clearly, the second law does not prevent systems from going from disorder to order. All the law does in this case is to make such mutations rare compared to mutations going in the thermodynamically favored direction—toward disorder. If that's all there were to it, however, gene systems would still eventually all move to a disordered nonfunctional state. They obviously don't. Is this because of a mystical precoded plan, or is there another, nonsupernatural explanation?

Now we come to the essence of evolution: natural selection. All that any organism has to do to escape "degeneration in accord with the second law of thermodynamics" is to be able to produce more young than are needed to replace the parents. As long as that is true, the occasional mutants (almost all less fit than the original version) will usually reproduce poorly or even die without adversely affecting the population. Since the harmful mutations are underrepresented in succeeding generations, these mutations simply cannot build up to a level that threatens the well-being of the population. Thus, mutations are random changes, usually toward disorder, but the effect of natural selection is to remove the relatively common disordered genes and prevent the genetic system from degenerating.

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In the same way, natural selection can replace genes with the rare mutant genes that represent an improvement over the original, thus serving as a type of ratchet to improve the organism and keep it matched to its changing environment. The entropy cost of the second law is paid as the energy required to produce those individuals that did not survive. The net result is that life opportunistically saves, builds upon, and improves whatever will function. At first glance, this may appear to conflict with the second law of thermodynamics, but the apparent conflict is not real. Therefore, no divinely precoded plan or mystical "vital force" is needed. Life and evolution are natural phenomena.


Lindsay, R. B. 1968. American Scientist. 56:100.

Morrison, P. 1978. in On Aesthetics in Science, ed. J. Weehsleo, p. 69. Cambridge: MIT Press.


By analogy, we can apply the same sort of reasoning that creationists apply to the second law to another law of nature: Water tends to flow downhill. Imagine a possible creationist perversion of this law: Water always flows downhill; it can never flow uphill. How can we test this?

One day, some years ago, I happened to swim in a river just below a rapids. To my amazement, the current started carrying me upstream! Eventually, I was propelled into the mainstream and carried in the direction the water intended to go. But in short order I found myself being carried upstream again.

Could it have been that I was in the grips of some supernatural force that was capable of circumventing the laws of nature? How could water go uphill?

Most of us recognize that I was in an eddy current or whirlpool. The rapidly flowing water going downhill on one side keeps the whirlpool spinning like a giant top. Indeed, the water on the outside away from the mainstream is being pushed upstream by the water flowing downstream in the main channel. The natural law about water flowing downhill has not really been broken after all. Were the river to dry up, the eddy current would disappear also. It "lives" at the expense of the river flow.

So it is that the universe and even the solar system is running downhill toward greater disorder. But certainly there are eddy currents here and there. Life itself is one of those eddies. As vast amounts of energy are dissipated from the sun and even the core of the earth, life captures a tiny proportion and uses that energy to run "uphill" for awhile, against the second law of thermodynamics—or so it seems.

William Thwaites

By William Thwaites and Frank Awbrey
This version might differ slightly from the print publication.