Mammoths dominated North America for thousands of years, then vanished within a few centuries at the end of the last Ice Age. NOVA lays out a new theory for that collapse alongside the old suspects: human hunters, a warming climate, and shrinking habitat. The film weighs the evidence each explanation would leave behind, from kill sites to pollen records, and tests whether any single cause fits the timing of the die-off across the continent. Researchers work through the case the way a detective would, ruling out possibilities that don't match the fossil record before settling on what does. The mammoth's disappearance stands in for a bigger question the episode keeps circling back to: what actually happens to a dominant species when its world changes faster than it can adapt.