Examining Y The evolution of human populations has long been studied with unique sequences from the nonrecombining, male-specific Y chromosome (see the Perspective by Cann ). Poznik et al. (p. 562 ) examined 9.9 Mb of the Y chromosome from 69 men from nine globally divergent populations—identifying population and individual specific sequence variants that elucidate the evolution of the Y chromosome. Sequencing of maternally inherited mitochondrial DNA allowed comparison between the relative rates of evolution, which suggested that the coalescence, or origin, of the human Y chromosome and mitochondria both occurred approximately 120 thousand years ago. Francalacci et al. (p. 565 ) investigated the sequence divergence of 1204 Y chromosomes that were sampled within the isolated and genetically informative Sardinian population. The sequence analyses, along with archaeological records, were used to calibrate and increase the resolution of the human phylogenetic tree.