It is an old-standing theory in evolutionary ecology: animal species on islands have the tendency to become either giants or dwarfs in comparison to mainland relatives. Since its formulation in the 1960s, however, the 'island rule' has been severely debated by scientists. In a new publication in Nature Ecology and Evolution on April 15, researchers solved this debate by analysing thousands of vertebrate species. They show that the island rule effects are widespread in mammals, birds and reptiles, but less evident in amphibians.