Mathematicians keep refining π even though they know it to more than 12 trillion digits; physicists beat themselves up because they cannot pin down the gravitational constant beyond three significant figures. Geneticists, by contrast, are having trouble deciding between one measure of how fast human DNA mutates and another that is half that rate. The rate is key to calibrating the 'molecular clock' that puts DNA-based dates on events in evolutionary history. So at an intimate meeting in Leipzig, Germany, on 25-27 February, a dozen speakers puzzled over why calculations of the rate at which sequence changes pop up in human DNA have been so much lower in recent years than previously. They also pondered why the rate seems to fluctuate over time. The meeting drew not only evolutionary geneticists, but also researchers with an interest in cancer and reproductive biology-fields in which mutations have a central role.
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