According to many (I cannot find a source at the moment), Albert Einstein's brain weighed less than average.
It is a common belief that there is no correlation between brain mass and intelligence. Is this true?
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Canadian researchers found a link between brain size and intelligence:
[they] examined the brains of 100 people who were given extensive IQ tests before they died and found a correlation between cerebral volume and intelligence.
The study looked specifically at the size of the cerebrum, the thinking part of the brain, and found a correlation with verbal intelligence in women. The same correlation was found for right-handed men.
This study found a link between the amount of grey matter and intelligence.
... the amount of gray matter in the frontal lobes turned out to be correlated with intelligence...
but this correlation doesn't necessarily mean causation, as seen in...
Cab drivers' grey matter enlarges and adapts to help them store a detailed mental map of the city, according to research.
Taxi drivers given brain scans by scientists at University College London had a larger hippocampus compared with other people.
The scientists also found part of the hippocampus grew larger as the taxi drivers spent more time in the job.
According to this
New research suggests that the layer of insulation coating neural wiring in the brain plays a critical role in determining intelligence.
The neural wires that transmit electrical messages from cell to cell in the brain are coated with a fatty layer called myelin. Much like the insulation on an electrical wire, myelin stops current from leaking out of the wire and boosts the speed with which messages travel through the brain--the higher quality the myelin, the faster the messages travel. These myelin-coated tracts make up the brain's white matter
Here you can read more about the difference between men and women.
Because brain size has been linked with intelligence, it's very tricky to go around saying that men have bigger brains. Yet men do seem to have women beat here; even when accounting for height and weight differences, men have slightly bigger brains. Does this mean they're smarter?
Men also have approximately 6.5 times more gray matter in the brain than women, but before the heads of all the men out there start to swell: Women have about 10 times more white matter than men do.
"These findings suggest that human evolution has created two different types of brains designed for equally intelligent behavior," said psychology professor Richard Haier of the University of California.
No, there is a substantial correlation between brain size and intelligence. The most current citation I know of is a paper from McDaniel 2005, titled: Big-brained people are smarter: A meta-analysis of the relationship between in vivo brain volume and intelligence
The abstract reads:
The relationship between brain volume and intelligence has been a topic of a scientific debate since at least the 1830s. To address the debate, a meta-analysis of the relationship between in vivo brain volume and intelligence was conducted. Based on 37 samples across 1530 people, the population correlation was estimated at 0.33. The correlation is higher for females than males. It is also higher for adults than children. For all age and sex groups, it is clear that brain volume is positively correlated with intelligence.
Not all brain regions are equal in contributing to this relationship however; the size of certain tracts, grey-matter tracts in the frontal cortex IIRC (it's been a while since I studied this myself) are the primary determiner of intelligence, as determined by IQ. Allometric scaling probably contributes to this correlation; for example, if a gene unleashes checks on brain growth to enable greater intelligence, it might have a pleiotropic effect on other regions, so that they have to grow bigger as well, though they don't directly contribute to the intelligence of the person whose brain they make up.