Autumn Leaves: The Search for Purpose

As the autumn leaves turn handsomely, I've been wondering, why do trees bother? It's a question scientists have been asking for the past few years, and for the first time, they've carried out an experiment to find out. The color of an autumn leaf can actually take a lot of work. In the fall, the green chlorophyll in a tree fades away, while the tree actively builds new pigments to turn it red or yellow. It's generally agreed that these colors must serve some function for trees. Otherwise, natural selection would favor drab trees that dropped their leaves without such bother. They could use the energy they didn't waste on autumn colors to fight diseases, capture more sunlight, or some other essential task. In 2001, the late biologist William Hamilton made a provocative proposal: he argued that leaves turned colors in the fall to warn off insects. Healthy trees could ...