averaging across all mammals, it follows a power law, with an exponent of about 0.75. this formula applies to the average brain of mammals but each family departs from it, reflecting their sophistication of behavior. for example, primates have brains 5 to 10 times as large as the formula predicts. predators tend to have larger brains. when the mammalian brain increases in size, not all parts increase at the same rate. the larger the brain of a species, the greater the fraction taken up by the neocortex.