Are Bigger Brains Smarter? Evidence From a Large-Scale Preregistered Study
Gideon Nave, Wi Hoon Jung, Richard Karlsson Linnér, Joseph W. Kable, Philipp D. Koellinger
Psychological Science
November 30, 2018
Although this experiment has been produced many times in the past, each time
concluding that there is a positive relationship between brain volume and intelligence, the
claim remains controversial. Publication bias and the lack of control for critical factors, such as
height, sex, age, socioeconomic status, etc., leads to skepticism of the results, so the
researchers have decided to gather 70% more participants than the combined participants of all
other experiments on the same question and control for the various variables that might have
an effect on the results. Thus, the scientific world will finally have an answer as to whether
larger brains lead to a larger display of intelligence and the controversy can be put to an end.
The results are important for studying other organisms and possibly determining their
intelligence with certain accuracy based solely on the size of their brain.
The researchers used 13,608 individuals from the United Kingdom who are all
genotyped who have anatomical MRI brain scans. The participants were given the fluidintelligence test, a 13 multiple-choice question exam that measured problem solving
independent of acquired knowledge. Participants would have two minutes to answer as many
of the 13 questions as possible and their score was the sum of the correct answers. Any
unanswered question would count as zero points and therefore not penalize the participant.
The test was given on three occasions: the first assessment visit, the second assessment visit,
and the imaging visit. The participants were never informed about their results on the tests.
Using images of the MRI brain scans that the participants took before partaking in the
experiment, the researchers were able to figure out the size/weight of everyone’s brain. The
researchers controlled for many of the variables listed in the introduction, as well as a few
more. Once all the factors were controlled for, the test results were compared with the sizes of
the matching person’s brain.
The researchers found a positive correlation between total brain volume and fluid
intelligence. After controlling for various variables, the correlation stayed the same, suggesting
a larger brain does in-fact lead to more intelligence. The model created by using the data
suggests that a 100-𝑐𝑚3 increase in total brain volume leads to an increase in the expected
fluid intelligence by about 0.14 standard deviations. The change is small, but relatively
significant when it comes to measuring intelligence. The results line up with many of the
previous studies that were conducted on the topic, despite their lack of control for as many
critical factors. This is because even when controlling for certain factors such as social status
and place of birth, the correlation did not change. As for education attainment, or the ability to
learn, understand, and remember information, the correlation with total brain volume was
smaller than the one for fluid intelligence. For comparison, a 100-𝑐𝑚3 increase in total brain
volume leads to an increase in expected schooling by about 0.4 years. Lastly, the researchers
found no significant difference in the correlation of total brain volume and fluid intelligence in
men and women.
Although the study does not answer a new question by any means, it looks to answer an
age-old question from a different perspective. Instead of solely focusing on total brain volume
and intelligence, the researchers tried to control for critical factors such as sex, age, height, and
genome. Thus, it would be clear if a larger brain was the true cause of a more intelligent person
or if the other experiments saw a positive correlation due to another variable or random
chance without knowing. However, even this experiment could be improved since all the
participants were from the United Kingdom and of European descent. Furthermore, many were
white, and all were past the age of 40. The experiment provides better proof that the
correlation does exist, but it is not yet perfect.