<P> There may be sex differences in the volume - IQ association . Some evidence suggests that while IQ correlates equally with frontal lobe volume, it may correlate more with parietal lobe volumes in men and with Broca's area in women, corresponding to spatial versus language specializations . </P> <P> Small studies have attempted to link brain volume with functional measures such as P300 auditory evoked potentials but finding no association . Studies attempting to related sibling differences in IQ to differences in brain volume are hampered by relatively small sample sizes and the noisy nature of such difference scores, yielding weak evidence for cross-trait cross-sib correlations . </P> <P> The largest brains are those of sperm whales, weighing about 8 kg (18 lb), and killer whales, weighing about 12--15 lb (5.4--6.8 kg). An elephant's brain weighs just over 5 kg (11 lb) and a bottlenose dolphin's 1.5 to 1.7 kg (3.3 to 3.7 lb). </P> <P> Brain size tends to vary according to body size . The relationship is not proportional, however; the brain - to - body mass ratio varies . The largest ratio found is in the shrew . Averaging brain weight across all orders of mammals, it follows a power law, with an exponent of about 0.75 . This power law formula applies to the "average" brain of mammals taken as a whole, but each family (cats, rodents, primates, etc .) departs from it to some degree, in a way that generally reflects the overall "sophistication" of behavior . Primates, for a given body size, have brains 5 to 10 times as large as the formula predicts . Predators tend to have relatively larger brains than the animals they prey on; placental mammals (the great majority) have relatively larger brains than marsupials such as the opossum . </P>

Who has the biggest brain in the world