Why do sperm whales have the largest brains of any animal?

Sperm whales have the largest brains of any living animal, weighing roughly 7 to 9 kilograms. Their brains are associated with complex social structures, vocal communication, and navigation during deep ocean dives. They live in matriarchal groups, use long-distance sound production, and hunt in deep waters where sensory and cognitive demands are high. A large brain is energetically expensive, so it likely persisted because it offered survival advantages. Scientists continue to study what brain size means for cognition in marine mammals.