User:MicroMacroMania/sandbox

Average adult male brain size is 1,345 gram, while an adult female have an average brain weight 1,222 gram. A baby's brain size at birth average 369 cc and increases, during the first year of life, to about 961 cc, after which the growth rate declines. Brain volume peak at the age of 40 and begin declining with 5% per decade, which begin speeding up at around 70. Adult twin studies have indicated high heritability estimates for overall brain size in adulthood (between 66% and 97%). The effect varies within the brain, however, with high heritabilities of frontal lobe volumes (90-95%), moderate estimates in the hippocampi (40-69%).

Studies demonstrate a correlation between brain size and intelligence, with larger brains predicting higher intelligence. It is however not clear if the correlation is causal. The majority of MRI studies report low correlations around 0.3 to 0.4 between brain volume and intelligence. The most consistent associations are observed within the frontal, temporal, and parietal lobes, the hippocampi, and the cerebellum, but only account for a relatively small amount of variance in IQ, which suggests that while brain size may be related to human intelligence, other factors also play a role. In addition, brain volumes do not correlate strongly with other and more specific cognitive measures.