House finches in Tucson, Arizona, have evolved longer, wider beaks to scarf down the sunflower seeds that pack backyard birdfeeders, and holy hawksbeard plants in Montpellier, France, make more seeds to cope with the city’s poor soil. Those are just a couple of the dramatic examples of urban evolution—which has affected everything from bedbugs to bobcats—researchers document in a review paper published today in Science. Roads and buildings prevent animals from moving from place to place, creating small, isolated populations that begin to differentiate—both physically and genetically—from each other, sparking evolutionary changes. But such barriers can also reduce the genetic diversity of a species, making it less resilient to threats such as climate change and disease. Even humans may be evolving. One study compiled by the review reveals that people in older cities are more resistant on a genetic level to such diseases as leprosy and tuberculosis, possibly because they descended from individuals who were better able to cope with these dangers.