The hypothesis that humans have a single origin was published in Charles Darwin's "The Descent of Man" (1871). The concept is supported by a study of present-day mitochondrial DNA, and with evidence based on physical anthropology of fossil humans. According to genetic and fossil evidence, older versions of "Homo sapiens" evolved only in Africa, between 200,000 and 100,000 years ago, with members of one branch leaving Africa by 90,000 years ago and over time replacing earlier human populations such as Neanderthals and "Homo erectus".