Getting Sexier All The Time

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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 and medicine. The authors of the swallow paper carried out a number of studies that suggest that the length of swallow tails is genetically based, and that those genes are changing. If they’re right–and other experts I contacted think they are–it’s a striking example of how quickly the sex lives of wild animals can evolve.

Things get a little fuzzier when the researchers propose what’s driving the evolution. They think desertification in the springtime range of the swallows in Algeria is to blame. But it’s very hard to eliminate other possibilities, since these swallows have complicated lives, migrating from Europe to South Africa and back every year. It’s much easier to make a case for the forces driving the evolution of Darwin’s finches, which generally sit obediently on the island on which they were born and are subject to cycles of droughts and heavy rains.

But it’s a question very much worth investigating. Global warming may well produce ecological changes that could produce just these sorts of rapid evolutionary changes in animals and plants. In some cases, species may be able to adapt quickly enough to their new environment. In other cases, they may lose the race.