When glaciers retreated at the end of the last ice age, populations of marine stickleback fish were stranded in newly formed lakes. Today, these remarkable little fish thrive in freshwater habitats drastically different from their ancestral ocean environment. The bodies of some lake stickleback populations have undergone a striking transformation, completely losing the long, projecting body spines that defend marine sticklebacks from large predators. This dramatic story of evolution is told in a beautiful short film featuring field locations in Alaska and the Nevada desert. Watch as scientists reveal changes in stickleback skeletons in living populations and the fossil record, and explain how we have come to understand that elements in our genomes, called genetic switches, play a powerful role in the evolution of bodies.