European eels spawn in the subtropical Sargasso Sea but spend most of their adult life in a range of fresh- and brackish waters, across Europe and Northern Africa. How eels adapt to such diverse environments has long puzzled biologists. Using whole-genome analysis, a team of scientists led from Uppsala University provides conclusive evidence that all European eels belong to a single panmictic population irrespective of where they spend their adult life, an extraordinary finding for a species living under such variable environmental conditions. The study is published in PNAS.