City dwellers have evolved bigger brains than their rural counterparts, a new study suggests—at least among white-footed mice and meadow voles. University of Minnesota biologist Emilie Snell-Rood looked at the skulls of 10 species of small mammals, and found that in those two species, specimens from urban environments had larger brain compartments than their rural counterparts, the New York Times reports.
It's not that the mice are taking in the big-city arts scene. Snell-Rood hypothesizes that humans forced the creatures to evolve by radically changing their habitat; only those who were the best at learning and adapting survived. Snell-Rood found the same kind of brain growth in two species of bats and shrews from rural environments that had also been dramatically changed by human activities. "The results are exciting," says one biologist, noting that Snell-Rood is the first to show animals' brain sizes increasing outside of labs. (Read more evolution stories.)