But Homo sapiens took a much quicker route to immunity—by interbreeding. Reproducing with another closely related species is an unintentional kind of biohacking: it immediately endows a species with gene variants that are already adapted to the new environment. Introgressed Neanderthal DNA was crucial in helping Homo sapiens to adapt to the new pathogens that they encountered as they migrated out of Africa. This process has been called the “poison-antidote model” of adaptive introgression: Neanderthals gave Homo sapiens a “poison” by exposing them to a novel pathogen, but also the “antidote”
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