Over 400 to 600 mouse generations, East and West Coast populations of European house mice have adapted to similar environmental conditions in very similar ways, research finds. The European house mouse has invaded nearly every corner of the Americas since colonizers brought it here a few hundred years ago, and it now lives practically everywhere humans store their food. Yet in that relatively short time span, populations on the East and West Coasts have changed their body size and nest building behavior in nearly identical ways, according to the study. To make these adaptations—at least in the case of body size—mice in the Western United States evolved many of the same genetic changes as their cousins in the East, showing that evolution often works on the same genes in different populations when those populations are confronted with similar environmental conditions.