Recent paleogenomic research revealed that interbreeding was common among early human species. However, little was known about when, where, and how often this hominin interbreeding took place. Using paleoanthropological evidence, genetic data, and supercomputer simulations of past climate, a team of international researchers has found that interglacial climates and corresponding shifts in vegetation created common habitats for Neanderthals and Denisovans, increasing their chances for interbreeding and gene flow in parts of Europe and central Asia.