Size does matter, study suggests

For more than a century some of the biggest minds in science have debated whether brain size has anything to do with intelligence. A new study suggests it does.

Bigger brains make for smarter people, says Michael McDaniel, an industrial and organizational psychologist at Virginia Commonwealth University.

"For all age and sex groups, it is now very clear that brain volume and intelligence are related," McDaniel said.

In the old days, measuring brain size involved either the imprecise method of putting a tape around a person's skull or waiting until they died to examine their noggins. Over the past five years or so, various research groups have studied brain size using new imaging techniques that provide a more accurate gauge.

McDaniel examined 26 mostly recent brain-imaging studies to reach his conclusion.

Still controversial is whether the standard intelligence tests used to measure smarts in the studies are valid. Do IQ tests really reveal intelligence? And how relevant are they to the real world?

"When intelligence is correlated with a biological reality such as brain volume, it becomes harder to argue that human intelligence can't be measured or that the scores do not reflect something meaningful," McDaniel said.

The work was published June 16 in the online version of the journal Intelligence.

The human mind eludes complete understanding, however.

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A study last year found that IQ is related to the amount of gray matter in the brain, and that intelligence does not reside in one location but is spread throughout the brain. Importantly, that research discovered that abundant gray matter in certain locations was strongly correlated to IQ.

"This may be why one person is quite good at mathematics and not so good at spelling, and another person, with the same IQ, has the opposite pattern of abilities," said that study's leader, Richard Haier of the University of California at Irvine.

Another investigation led by Haier and reported earlier this year found that men think more with their gray matter and women tend to rely more on white matter, the other primary type of brain tissue.

McDaniel works with employers to screen job applicants and measure their performance. He now thinks intelligence tests are the single best predictor of job performance.

"On average, smarter people learn quicker, make fewer errors, and are more productive," McDaniel said. "The use of intelligence tests in screening job applicants has substantial economic benefits for organizations."