I have a short piece in today’s New York Times about how male swallows are evolving longer tails, which female swallows find sexy. Here’s the original paper in press at The Journal of Evolutionary Biology. Measuring the effects of natural selection is tough work, the details of which are impossible to squeeze into a brief news article. Scientists have to document a change in a population of animals–the length of feathers, for example–but then they have to determine that the change is a product of genetic change. We are much taller than people 200 years ago, but it’s clear that most, if not all, of this change is simply a response of our bodies to better food