Neanderthals and Denisovans regularly interbred

SET aside romantic sentiment. Sex is a biological insurance policy. By chaotically mixing their genetic information, animals generate extraordinary diversity. In general, the more different the genomes of the partners are, the greater the diversity in their offspring and the more likely it is that some of the combinations will survive. Early humans had no inkling of evolutionary theory. But the discovery of a teenage girl with a Neanderthal mother and a Denisovan father shows they were happily participating in the practice.A team led by Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology, in Leipzig, Germany, carried out genetic analysis on a fragment of bone, more than 50,000 years old, found in a cave in Russia. It came from a girl, aged about 13, who seemed to belong to the Denisovans, a poorly understood cousin of modern humans who evolved in Eurasia around 390,000 years ago and then were driven into extinction some 40,000 years ago.