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Wednesday, February 22, 2012

Evolution and Entropy: The Magic of Sunlight

Does the second law of thermodynamics pose a problem for evolution? Daniel Styer doesn't think so. In fact, in a recent paperhe found that any entropy decrease here on Earth due to evolution would have been dwarfed by the entropy increase of solar radiation contributing to the cosmic microwave background. He writes:

Presumably the entropy of the Earth’s biosphere is indeed decreasing by a tiny amount due to evolution, and the entropy of the cosmic microwave background is increasing by an even greater amount to compensate for that decrease. But the decrease inentropy required for evolution is so small compared to the entropy throughput that would occur even if the Earth were a dead planet, or if life on Earth were not evolving, that no measurement would ever detect it.
In other words, entropy is a non issue. In fact, Styer shows it is a non issue by 12 orders of magnitude (it is actually 14 orders of magnitude but Styer makes a calculation error). How does he arrive at this conclusion? Styer compares individuals separated by 100 years and uses a factor of 1000 times reduction in microstates. This nicely turns out to solve the problem.

Interestingly Styer says his selection of a reduction factor of 1000 is "very generous." One can hardly argue with that. Am I 1000 times less likely than my great grandfather? Of course not.

But why not go further to strengthen the case? Styer could increase the factor to 100000 or 10^6, or 10^12, or 10^50, or 10^99, or ..., without harming the case. With Styer's method one could assume individuals separated by 100 years have a reduction in microstates that is tens or hundreds of orders of magnitude beyond Styer's "very generous" assumption. Styer could have made a "very, very, very, very, very ... generous" assumption and still reveal entropy to be a non issue.

But of course this would have revealed the silliness. Every individual, in every species, for all history could be 10^99 more improbable than an individual from a century earlier, and you're nowhere close to a problem. Amazing what a little sunlight does.

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