Wednesday, June 01, 2005

Entropy and Evolution

A couple of items related to the idea that evolution is somehow prohibited by the second law of thermodynamics popped up the radar screen lately. The first is an Evolutionblog critique of such an argument defended by mathematician Granville Sewell. The second is a new article posted by Babu G. Ranganathan at Intellectualconservative.com.

The general argument begins with a demonstration that disorder, as measured by the thermodynamic entropy, must always increase under certain sets of conditions. Once this point is established, this increase in disorder is contrasted with the apparent increase of order with time observed in the history of life on Earth. The apparent contradiction is resolved by asserting that Darwinian evolution in some or all respects is false.

As you might have expected, these arguments have led to mass levels of discussion about the thermodynamic properties of various systems, usually distinguished from one another in terms of whether they are isolated or "open" to their environments. The properties of such systems aside, it seems to me that there is an extremely serious error with these entropy arguments against evolution, namely that the thermodynamic entropy is only defined for equilibrium states of a system. Life forms such as cells that are generating a steady flow of heat into their environments through the metabolism of food are not in thermodynamic equilibrium. Arguments about the entropy of such life forms cannot contradict theories of evolution because an entropy cannot be defined in the first place.

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