A female Anopheles quadrimaculatus mosquito takes a blood meal from a host. For millennia, this mosquito has spread malaria. Researchers now think that these mosquitoes — and the disease they carry — played a critical role in determining where ancient humans settled and whether they thrived or failed to thrive. Smith Collection/Gado via Getty Images hide caption

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Smith Collection/Gado via Getty Images

For tens of thousands of years, where humans have chosen to live has long been shaped by climate and the landscape. That's why there are so few of us clinging to the crags of Mount Everest or decamping to Antarctica.…