Three-spined sticklebacks live in both salt and fresh water. When the glaciers melted at the end of the last ice age and new lakes were formed, sticklebacks from the sea found new habitats in them. Felicity Jones and her team at the Friedrich Miescher Laboratory of the Max Planck Society in Tübingen are investigating how the genome of the fish changes in the course of adaptation. 12,000-year-old stickleback bones provide insights into the early stages of this process.