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the order, we see on Earth. What really needs to be explained is the fact that adaptation here on Earth produces so much disorder. The second law does exactly this by allowing adaptations, but only on the condition that their appearance increases entropy. Any process competing with natural selection as the source of adaptations has to produce adaptations from nonadaptations, and every one of the adaptations it produces will have to be rare, expensive, and wasteful. We’ll see that this requirement—that building and maintaining orderliness always has to cost more than it saves—rules out all of natural selection’s competitors as the source of adaptation, diversity, and complexity.

Could there be a process that produces adaptations that is less wasteful than the particular way in which Darwinian natural selection operates on Earth? Probably. How wasteful such a process can be depends on the starting materials and on how much variation emerges in the adaptations built from them. But every one of these possible processes has to rely on dumb luck to produce the first sliver of an adaptation. In that respect, they would still just be more instances of the general process Darwin discovered—blind variation and environmental filtration. A process that explained every later adaptation by more dumb luck shuffling and filtering of the earlier adaptations would still be Darwinian natural selection. It would be Darwinian natural selection even if the process was so quick and so efficient as to suggest that the deck was stacked. So long as the deck wasn’t stacked to produce some prearranged outcome, it’s still just blind variation and environmental filtration. Any deck stacking—a process of adaptive evolution that started with some unexplained adaptation already in the cards—is ruled out by physics.

ONLY THE SECOND LAW CAN POWER

ADAPTIVE EVOLUTION

The second law’s demand for persistent increase in entropy makes natural selection the only game in town, but there is another, deeper reason why it does so. No matter what brings it about, the process of adaptation is different from the more basic physical and chemical processes in nature. They are all “time symmetrical.” Adaptation is not. But the only way a time-asymmetrical process can happen is by harnessing the second law.

As you may recall from Chapter 2, a time-symmetrical process is reversible. Chapter 2 provided one example: any set of ricochets on a billiard table can be reproduced in exactly the opposite order. Here are some more examples: Hydrogen and oxygen can combine to produce water, but water can also release hydrogen and oxygen. Even the spreading circular waves made when a drop of liquid falls into a pool can be reversed to move inward and expel the drop upward from the surface. No matter in what order the basic chemical and physical processes go, they can go in the reverse order, too.

The second law creates all asymmetrical processes and gives them their direction in time. Now, the evolution of adaptations is a thoroughly asymmetrical process. Take a time-lapse film of a standard natural selection experiment. Grow bacteria in a petri dish. Drop some antibiotic material into the dish. Watch the bacterial slime shrink until a certain point, when it starts growing again as the antibiotic resistant strains of the bacteria are selected for.

Now try reversing the time-lapse video of the process of bacterial selection for resistance. What you will see just can’t happen. You will watch the population of the most resistant strain diminish during the time the antibiotic is present. After a certain point, you will see the spread of the bacteria that can’t resist the antibiotic, until the drops of the antibiotic leave the petri dish altogether. But that sequence is impossible. It’s the evolution of maladaptation, the emergence, survival, and spread of the less fit.

There is only one physical process available to drive asymmetrical adaptive evolution. That is the asymmetrical entropy increase the second law of thermodynamics requires. Therefore, the second law must be the driving