In this review, Taichi Suzuki takes on the challenge of thinking through how the microbiome can play a role in the process of human genetic adaptation to new environments. When humans spread out across the globe they encountered new diets, climates and pathogens. The history of those encounters in written into human genomes across the world. How did the microbiomes interact with these new challenges to shape the human genome locally? Find the full review in the 04 December issue of Science.