Which Animal Has the Largest Brain?

The sperm whale (Physeter macrocephalus) brain averages about 7.8 kg, the heaviest of any living or extinct animal. However, brain size alone does not determine intelligence — what matters more is the brain-to-body-mass ratio (encephalisation quotient, or EQ). Humans have the highest EQ among large mammals, with brains about 7 times larger than expected for our body size. Dolphins and great apes also have high EQs. Sperm whale brains, while enormous, are proportionally smaller relative to their 50-tonne body. The sperm whale brain has a highly developed limbic system (associated with emotions and social behaviour), consistent with their complex social structures — females live in stable family groups and cooperatively care for young. Elephant brains, at about 5 kg, are the second heaviest and contain roughly 257 billion neurons — three times the 86 billion in a human brain — though their distribution differs significantly.