WE have generated over 100 kilobases of sequence from the nonrecombining portion of the Y chromosomes from five humans and one common chimpanzee. The human subjects were chosen to match the earliest branches of the human mitochondrial tree. The survey of 18.3 kilobases from each human detected only three sites at which substitutions were present, whereas the human and chimpanzee sequences showed 1.3% divergence. The coalescence time estimated from our Y chromosome sample is more recent than that of the mitochondrial genome. A recent coalescence time for the Y chromosome could have been caused by the selected sweep of an advantageous Y chromosome or extensive migration of human males.