Neanderthals and Denisovans as biological invaders

Humans stand out among our close primate relatives as effective biological invaders. Our recent history has included range expansions into remote and harsh geographic regions, and invasions by some populations into areas long occupied by others. Historians tend to frame these events as a story of technological and economic progress, while admitting that disease sometimes plays a central part—a triad made memorable by Guns, Germs, and Steel: The Fates of Human Societies (1). Ancient DNA is revealing a deeper prehistory of human dispersals, however, showing continuity with invasions as understood by biologists, not just historians. Now, in PNAS, Rogers et al. (2) find that not only modern humans but also Neanderthals and Denisovans may share a surprisingly invasive origin. The story of Neanderthal and Denisovan origins has developed rapidly during the past 7 y. Two high-coverage genomes, and more fragmentary genome data from a handful of other individuals, have yielded powerful insights about the diversity of these ancient groups and their legacy of genetic introgression into recent humans (3). These archaic populations share a deep common history, and individual genomes record a history of high inbreeding and low gene flow across their ancient geographic ranges (4, 5). In their new study, Rogers et al. (2) find that the common ancestral population of the Denisovans and Neanderthals underwent a tight bottleneck, immediately after this population diverged from the African ancestors of modern humans. This bottleneck was rapid, maybe only 300 generations, and the Neanderthal and Denisovan populations separated quickly thereafter. This archaic human dispersal, which unfolded more than 600 ka, bears a striking parallel to the much later dispersal of modern humans from Africa into Eurasia after 100 ka. In both cases, the small bottleneck is etched into the genomes of all their descendants, and in both cases, this founder … [↵][1]1Email: jhawks{at}wisc.edu. [1]: #xref-corresp-1-1