The fall colors are long gone in Wisconsin, but another new favorite blog (The Loom) is paying tribute to William Hamilton's attempt to explain fall colors as an evolutionary adaptation.

He and Brown proposed that a brilliant leaf was, like a peacock's tail, a signal. A peacock's tail takes a huge investment of energy, energy that could otherwise be diverted to fighting off parasites or surviving other stresses. A strong male can afford to use up this energy, which makes the tail an honest ad for its parasite-fighting genes. In the case of leaves, trees are not sending signals to other trees--they are sending signals to tree-eating insects.

Trees, after all, are as besieged by insects as birds or other animals are by internal parasites. They fight their enemies a sophisticated arsenal of chemical agents, sticky traps, and other weapons of mass arthropod destruction. Hamilton and Brown proposed that trees that have a strong constitution warn off insects by changing colors in the fall. In a sense, they say, "I can shut down my photosynthesis early in the fall, pump a lot of red or yellow pigments into my leaves, and still have enough energy left to annihilate your babies when they hatch in the spring. So just move along."

Now, I am not a biologist (though I did read parts of The Structure of Evolutionary Theory!), but this strikes me as at least a little far-fetched. It reminds me of the old expression, "when you have a hammer, every problem looks like a nail." I have another explanation for fall colors: they just happen as the leaves die. It's going to take more than 100 birch trees in Norway to convince me otherwise.

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