Does evolution contradict the second law of thermodynamics? (Intermediate)

I probably won't get an answer to this one..... but entropy says the universe is breaking down... evolution says the universe is getting better! Please explain this.

This idea has been put forward by many people to try to prove that evolution is impossible. However, it is based on a flawed understanding of the second law of thermodynamics, and in fact, the theory of evolution does not contradict any known laws of physics.

The second law of thermodynamics simply says that the entropy of a closed system will tend to increase with time. "Entropy" is a technical term with a precise physical definition, but for most purposes it is okay to think of it as equivalent to "disorder". Therefore, the second law of thermodynamics basically says that the universe as a whole gets more disordered and random as time goes on.

However, the most important part of the second law of thermodynamics is that it only applies to a closed system - one that does not have anything going in or out of it. There is nothing about the second law that prevents one part of a closed system from getting more ordered, as long as another part of the system is getting more disordered.

There are many examples from everyday life that prove it is possible to create order! For example, you'd certainly agree that a person is capable of taking a pile of wood and nails and constructing a building out of it. The wood and nails have become more ordered, but in doing the work required to make the building, the person has generated heat which goes into increasing the overall entropy of the universe.

Or, if you prefer an example that doesn't require conscious human intervention, consider what happens when the weather changes and it gets colder outside. Cold air has less entropy than warm air - basically, it is more "ordered" because the molecules aren't moving around as much and have fewer places they can be. So the entropy in your local part of the universe has decreased, but as long as that is accompanied by an increase in entropy somewhere else, the second law of thermodynamics has not been violated.

That's the general picture - nature is capable of generating order out of disorder on a local level without violating the second law of thermodynamics, and that is all that evolution requires.

The idea of evolution is simply that random genetic mutations will occasionally occur that lead an individual organism to have some trait that is different from that of its predecessors. Now, it is true that these mutations, being random, would probably tend to increase the "entropy" of the population as a whole if they occurred in isolation (i.e., in a closed system). That is, most of the mutations will create individual organisms that are less "ordered" (i.e., less complex) and only some will create individual organisms that are more complex, so overall, the complexity goes down.

However, evolution does not take place in a closed system, but rather requires the existence of outside forces - i.e., natural selection. The idea is that there can be some environmental effect that makes organisms with a particular mutation (one that makes them more "complex") more likely to survive and pass their genes on to the next generation. Thus, as generations go by, the gene pool of the species can get more and more complex, but notice that this can only occur if the gene pool interacts with the outside world. It is through the course of that interaction that some other form of entropy (or disorder) will be generated that increases the entropy of the universe as a whole.

If the above is too esoteric, consider a simple analogy: a poker tournament. In poker, good hands are less likely to be dealt than bad ones - for example, the odds of getting three of a kind are much less than the odds of getting two of a kind. So in a poker tournament, most people will be dealt bad hands and only a few will be lucky enough to be dealt good hands. But it is the people with good hands who will be more likely to win and "survive" to the next round. So the "outside forces" (in this case, the rules of poker) acting on a random distribution (all the poker hands that were dealt) will tend to select out the best, least likely ones.

For further information, the Talk.Origins website has an extensive discussion about the evolution/thermodynamics controversy.

This page was last updated June 27, 2015.

About the Author

Dave Rothstein

Dave is a former graduate student and postdoctoral researcher at Cornell who used infrared and X-ray observations and theoretical computer models to study accreting black holes in our Galaxy. He also did most of the development for the former version of the site.

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