The expanding global human footprint is dividing the world’s flora and fauna into ever-smaller, more isolated populations that could wink out because of inbreeding, disease, or environmental change. For decades, conservationists have proposed revitalizing those holdouts by bringing in new blood from larger populations. But they’ve wondered whether it really works—and how to do it without swamping the genetic identity and unique adaptations of the group at risk. Last month at Evolution 2019 here, researchers described how genomic tools are refining what is known as genetic rescue.