ananyo writes "Black cottonwood trees (Populus trichocarpa) can clone themselves to produce offspring that are connected to their parents by the same root system. Now, after the first genome-wide analysis of a tree, it turns out that the connected clones have many genetic differences, even between tissues from the top and bottom of a single tree. 'When people study plants, they'll often take a cutting from a leaf and assume that it is representative of the plant's genome,' says Brett Olds, a biologist at the University of Illinois at Urbana-Champaign who was involved in the study. 'That may not be the case. You may need to take multiple tissues.' The finding also challenges the idea that evolution only happens in a population rather than at an individual level. As one tree contains many different genomes, natural selection and evolution could happen within a single organism."