The earliest evidence of TB comes from skeletons buried in the Middle East 9000 years ago, soon after the invention of agriculture. But the variant that kills humans today—Mycobacterium tuberculosis—emerged 2000 years ago, when people lived in denser settlements alongside domesticated animals, often reservoirs for TB. Two years ago, University of Paris graduate student Gaspard Kerner discovered people were at much higher risk of getting severely ill when infected with TB if they inherited two copies of a rare variant of the immune gene TKY2, called P1104A. He realized that by tracing the frequency of that variant in 1013 European genomes from the past 10,000 years, he had a “golden” tool to detect how the immune gene coevolved with TB, says Quintana-Murci, who hired Gaspard as a postdoc at the Pasteur Institute.