encephalization quotient

The encephalization quotient, or EQ, is a number that tells you whether an animal's brain is bigger or smaller than you would expect for a creature of its body size. Big animals tend to have big brains simply because a large body needs more nerves to run it, so raw brain weight alone is misleading. EQ fixes this by comparing an animal's actual brain size to the size a typical animal with the same body weight would have, then dividing the first by the second. An EQ of 1 means exactly average; above 1 means more brain than expected; below 1 means less.

Think of it like grading a city's bus fleet not by the raw number of buses, but by how many buses it has compared to other cities of the same population — that ratio reveals whether the city is unusually well served. By this measure humans score around 7, meaning our brains are roughly seven times larger than expected for an animal our size, which is the highest of any species. Dolphins, chimpanzees, and elephants also score well above 1. Researchers use EQ as a rough proxy for intelligence and cognitive capacity, because the brain tissue left over after running the body is the part free to handle thinking, learning, and complex behavior.