Do bigger brains mean higher intelligence?

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People with larger brains tend to score higher on intelligence tests. But the link is modest. A bigger brain does not automatically mean a more intelligent person.

Why the idea can seem plausible

A researcher quoted by Penn proposed that more neurons might help with memory. More neurons might also help with doing several tasks at once. The researcher compared this with computers: more transistors could let computers calculate faster. That is a proposed explanation. It has not been shown to explain how the link works. The claim also has real evidence behind it. Studies repeatedly link larger brains with higher scores, though the link is usually small.

Do larger brains really go with higher scores?

Researchers usually measure brain volume (the space the brain fills) using MRI, a type of scan. A 2015 meta-analysis combined results from 148 samples covering over 8,000 people. It found a positive link with IQ. IQ tests compare general intelligence with that of people the same age. The analysis's authors warned that publication favoured stronger results. But the positive link survived their checks for this skew in what gets published.

The 2019 UK Biobank study included 18,426 people aged 44–81 with scans and at least one thinking test. After accounting for age and sex, the correlation (a measure of the link) was 0.276. This showed a modest tendency for people with larger total brain volumes to score higher. Its authors caution that the volunteers studied and their age range may limit how widely the result applies.

ZPID's account of a 2022 review reports a small correlation of 0.23. This covered 143 studies involving over 26,000 people. This result comes through ZPID's summary. The summary says it does not verify the review authors' scientific claims. The 2019 UK Biobank paper reports results from a reanalysis (a fresh analysis) involving healthy adults. In that analysis, studies with better-quality intelligence tests tended to show stronger links between brain volume and intelligence.

Does bigger mean smarter regardless of body size or sex?

Penn reports that the study it describes accounted for height, sex, age, and social and economic background. It also accounted for population differences measured through genetics.

A review describes large differences in average brain size between sexes. Alongside these, differences in average intelligence are very small or absent. The 2019 UK Biobank study also found no sex difference in the strength of the volume–intelligence link.

Does size cause intelligence?

How the link works remains uncertain. A 2019 study's authors interpreted genetic patterns as consistent with brain size influencing intelligence. These patterns linked volume inside the skull and years of education. That interprets the link as cause and effect. It is not a settled explanation. The researcher quoted by Penn also suggested parenting as a possible alternative explanation for the size–score link. That, too, was a proposed explanation.

Does a bigger head mean the same thing?

A head measurement is different from a brain scan. A 2024 review examined studies measuring around children's heads before age 20. Only 21 of 115 met its minimum quality standards. Among intelligence studies of the general population that met those standards, 12 of 16 found positive links. The review examined the link between head circumference (distance around the head) and intelligence in the general population. It found evidence that this link may not follow a straight line. More than 80% of all included studies had serious limitations.

Official information, with dates

MedlinePlus Genetics was updated 1 August 2023. It describes how both genes and the environment influence intelligence. MedlinePlus's A.D.A.M. reference entry on IQ testing was reviewed 20 October 2024. It warns that tests may miss talents and future potential. Its head-circumference entry was reviewed 17 January 2025.

An archived NIMH research release dated 31 May 2018 describes different organisational needs of larger brains. It does not establish that bigger is better. ZPID's summary, dated 28 October 2024, warns against automatically judging intelligence from size.

What people also ask

Do people with higher IQ have bigger brains?

There is a tendency in that direction. But the link does not reliably tell you how intelligent one person is.

Does IQ affect brain size?

The link alone does not establish that IQ affects brain size. How the link works remains unresolved.

Do high IQ brains look different?

Higher scores are linked with greater total brain volume. But overall size alone says little about brain complexity.

Is head size related to IQ?

Among intelligence studies of the general population meeting the review's minimum quality standards, 12 of 16 found positive links. But the review also found evidence that the link may not follow a straight line. It also found substantial study limitations.

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