Driving home at the end of the long weekend, I was amazed to see a tree here and there along the road with a touch of orange in its leaves. Fall already. And with fall comes another team of scientists to puzzle over why leaves change color.

I’ve been following this story for four autumns now, both in the New York Times, and in a series of blog posts (one, two, three, and four). It began with a simple question from one of the great evolutionary biologists since Darwin. William Hamilton argued that it takes a lot of energy for autumn leaves to produce the brilliant pigments that make fall so beautiful. Why bother, Hamilton asked.