Big Idea

Evolution doesn't just build — it also un-builds. On predator-free islands, birds shed flight and fear. In isolated seas, gentle giants grew enormous. In distant continents, unrelated mammals sculpted near-identical bodies. These are some of the most extraordinary products of natural selection — and some are gone forever. But others, reduced to mere handfuls of survivors, have been pulled back from the edge. This lesson is about what made these animals remarkable, and what their stories reveal about evolution.