Bats are shy creatures, especially during the daytime, when they hide in caves, trees, and even under bridges. Yet when it comes to Darwinian success, they are anything but low-profile: Bats make up one out of every five mammalian species. And they are innovative as well, being the only mammals to fly under their own power. A new study pins this airy achievement on a bone growth gene, whose boosted expression may have literally helped bats sprout wings and take off.