You have to hand it to those little flu viruses–with just a few genes apiece, they can infect us humans by the millions, and we can barely keep up with their evolution. In tomorrow’s New York Times, I’ve written a natural history of the flu, looking at how influenza viruses mutate, swap genes, undergo natural selection, cross species barriers, and  adapt to new hosts. The new strain of swine flu (or perhaps more precisely, the new strain of human-and-bird-flu-viruses-swirled-up-inside-pigs-and-then-mixed-with-other-pig-viruses-that-descend-from-human-and-bird-flus-as-well) is just the latest chapter in this baroque evolutionary tale.