Larger brains do not lead to high IQs

brain
Left hemisphere of J. Piłsudski's brain, lateral view. Credit: public domain

As early as 1836, the German physiologist and anatomist Friedrich Tiedemann, in an article in the Philosophical Transactions, expressed his opinion that "there is undoubtedly a connection between the absolute size of the brain and the intellectual powers and functions of the mind". 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.

Now, an international team of researchers, led by University of Vienna researchers Jakob Pietschnig, Michael Zeiler, and Martin Voracek from the Faculty of Psychology, together with Lars Penke (University of Göttingen) and Jelte Wicherts (Tilburg University), published a meta-analysis examining correlations between in-vivo and IQ in Neuroscience and Biobehavioral Reviews. Based on the data from 148 samples comprising over 8000 participants, they report a robust but weak association between and IQ. This association appeared to be independent of participant sex and age.

"The presently observed association means that brain volume plays only a minor role in explaining IQ in humans. Although a certain association is observable, brain volume appears to be of only little practical relevance. 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.

Brain structure vs. brain size

The importance of brain structure compared to brain volume becomes already evident when comparing different species. When considering absolute brain size, the sperm whale weighs in with the largest central nervous system. When controlling for body mass, the shrew is on the top of the list. Similar results emerge when considering other aspects of species anatomy: Homo sapiens never appears at the top at the list, as would be expected. Rather, differences in appear to be mainly responsible for between-species differences in cognitive performance.

Within Homo sapiens, there are indications that render a large association between IQ and brain volume similarly questionable. For instance, differences in brain size between men and women are well-established, yielding larger brains of men compared to women. However, there are no differences in global IQ test performance between men and women. Another example are individuals with megalencephaly syndrome (enlarged brain volume) who typically show lower IQ test performance than the average population. "Therefore, structural aspects appear to be more important for cognitive performance within humans as well", concludes Jakob Pietschnig.


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More information: Pietschnig, J., Penke, L., Wicherts, J. M., Zeiler, M., & Voracek, M. (2015). Meta-analysis of associations between human brain volume and intelligence differences: How strong are they and what do they mean? Neuroscience and Biobehavioral Reviews, in press. DOI: dx.doi.org/doi:10.1016/j.neubiorev.2015.09.017
Citation: Larger brains do not lead to high IQs (2015, October 14) retrieved 16 July 2019 from https://medicalxpress.com/news/2015-10-larger-brains-high-iqs.html
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HTK
Oct 14, 2015
LOL

Just cos orientals have by average 10% bigger brains!

whale brain size with another whale of the same species does matter.

Oct 15, 2015
Agree. Then what is behind intelligence? Glial cells.

Oct 15, 2015
148 samples from 8000 participants is hardly exhaustive proof, one would hope for a larger sample size comprized from different racial groups world wide.
In spite of all the boring provisos, perhaps written for for that subnormal group of humans known as journalists, and all the ifs ands or buts, one still has to take away from this article a seeming probability that , "Based on the data from 148 samples comprising over 8000 participants, they report a robust but weak association between brain size and IQ. "
One really gets bored by the politically correct "protecting one's ass" rhetoric, which only weakens the world of science. It's time that scientists had the guts to robustly report their finding, without all the queasy "don't beat me because I didn't find results to make Social Justice Warriors happy" provisos.
Any particular man woman black white yellow person may be at any level of imbecility or genius, and must be treated equally. Groups of people will average differently

Dug
Oct 17, 2015
Earlier work does show differences between men and women. Men produce more geniuses, but also more sub-intelligent. There are also many differences in specific tasking between male and female brains.

This is a rather gross review of a complex subject, though end product may be quite correct. Structure is more closely associated with higher intellectual performance than volume. Earlier work also showed that Einstein's brain was average volume, though its structure was more complex than normal.

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