"While it is tempting to interpret this association in the context of human cognitive evolution and species differences in brain size and cognitive ability, we show that it is not warranted to interpret brain size as an isomorphic proxy of human intelligence differences," the researchers conclude in Neuroscience and Behavioural Reviews. An international team of researchers from the Universities of Vienna (Austria), Göttingen (Germany), and Tilburg (Netherlands) provides no evidence for a causal role of brain size for IQ test performance. But a review of 88 studies involving more than 8,000 participants has now shown that even though a small link between brain volume and IQ exists, there's no evidence to suggest it's a causal one. With the advent of brain imaging methods (e.g., MRI, PET), reliable assessments of in-vivo brain volume and investigations of its association with IQ are now possible. But regardless, Pietschnig and his team showed that there was still a weak association between bigger brains and higher IQs throughout the research, which was independent of sex and age - but they also showed that brain size didn't have much predictive value when it came to measuring intelligence. "The presently observed association means that brain volume plays only a minor role in explaining IQ test performance in humans. "Although a certain association is observable, brain volume appears to be of only little practical relevance," said lead researcher Jakob Pietschnig, from the University of Vienna in Austria. Rather, brain structure and integrity appear to be more important as a biological foundation of IQ, whilst brain size works as one of many compensatory mechanisms of cognitive functions", explains Jakob Pietschnig from the Institute of Applied Psychology of the University of Vienna. Their conclusion is supported by the fact that men consistently have higher brain volumes than women, but that there's no significant difference between the sexes when it comes to IQ tests. This is because of publication bias, which means that journals are more willing to publish papers that find a strong link between something rather than those that find a small one, or are inconclusive.
– If brain size relative to body size determines IQ, the venerable shrew would be the smartest creature on the planet. But it doesn't, and it's not, and scientists from Austria, the Netherlands, and Germany have combed through 88 studies with more than 8,000 participants to confirm in the journal Neuroscience and Behavioral Reviews that when it comes to intelligence, brain size simply doesn't matter. "Although a certain association is observable, brain volume appears to be of only little practical relevance," says Jakob Pietschnig from the Institute of Applied Psychology at the University of Vienna. The researchers write that "positive associations between human intelligence and brain size have been suspected for more than 150 years." Why the long-held belief in such a link despite a lack of concrete evidence for it? It may partly be the result of publication bias, reports ScienceAlert. This means that journals more readily publish findings with strong links between subjects than weak or inconclusive links. And that's all that Pietschnig and his team found when they reviewed published and unpublished studies—a link too small to have any discernible effect. "Rather, brain structure and integrity appear to be more important as a biological foundation of IQ, whilst brain size works as one of many compensatory mechanisms of cognitive functions," Pietschnig adds. This helps explain why men, who tend to have larger brains than women, do not perform better on IQ tests. To be small-minded, then, should be construed in only a metaphorical sense. (Check out what has been hiding in brains for centuries until this year.)