ou might think, with the completion of the Human Genome Project more than 20 years ago, and the discovery of the double helix enjoying its 70th birthday last year, that we actually know how life works. In physics, the quest for a so-called Grand Unifying Theory has preoccupied the most ambitious minds for generations, alas to no avail. But in the life sciences, we managed to find four grand unifying theories in the space of 100 years or so. Three are well
