Brain size area in women, corresponding to spatial versus language specializations. 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. The largest brain is that of the sperm whale, weighing about , and killer whales, weighing about . An elephant's brain weighs just over and a bottlenose dolphin's . Brain size tends to vary according
Human brain hippocampi, and the cerebellum, but these only account for a relatively small amount of variance in IQ, which itself has only a partial relationship to general intelligence and real-world performance. Other animals, including whales and elephants have larger brains than humans. However, when the brain-to-body mass ratio is taken into account, the human brain is almost twice as large as that of a bottlenose dolphin, and three times as large as that of a chimpanzee. However, a high ratio does not of itself demonstrate intelligence: very small animals have high ratios and the treeshrew has the largest quotient of any