Tracing single-cell histories

DNA mutations accumulate at a steady pace across the human genome, passing from one generation to another. On the basis of the degree of shared mutations, a genealogical relationship can be reconstructed from ancient and modern individuals, allowing one to go back hundreds of thousands of years in human evolutionary history (1). Instead of comparing individuals, on pages 550 and 555 of this issue, Bae et al. (2) and Lodato et al. (3), respectively, assessed the rate of DNA mutation in single cells from developing and aging human brains, revealing mutational histories in neurodevelopment, aging, and neurodegeneration. These approaches also have implications for understanding complex diseases that could result from somatic mutations that arise later in life, such as cancer