The genetic factors that influence how big your brain is may also determine how smart you are, a recent Duke study suggests.

A recent Duke study tested associations between participants’ genetics, total brain volume and intelligence by analyzing previous data on brain size, as well as on the genetics of educational attainment. 

“We just wanted to know if one of the biggest predictors of intelligence in the brain, which is brain size, was one of the mechanisms through which these genes might influence later educational ability and IQ because those things are fairly highly genetically correlated," said lead researcher Maxwell Elliott, a clinical psychology Ph.D. student.

The researchers used data from genome-wide association studies (GWAS), which contained information on the genetic variance associated with educational attainment of thousands of people.

They focused on data concerning the genetics of educational attainment and the highest level of education completed. This is because IQ and educational attainment are directly correlated, and the GWAS sample sizes for educational attainment are much bigger.

The idea was to look at the connection between brain size and intelligence, and the best way to look at intelligence with the greatest set of data is by looking at the genetics of educational attainment. 

“We used the information from these big studies to try to understand the genetics that influence educational attainment and what kind of biological thing in the brain might be in between that association," Elliott explained.

Prior to this study, Elliott and his team already knew about links between education attainment and intelligence, as well as between brain size and intelligence. 

From there, they wanted to analyze the genetic predictors outlined in the GWAS of educational attainment in order to map out the process beginning with genetics and ending with the outcome of intelligence.

In between one’s genetic predictors of intelligence and their actual intelligence are several factors, including the brain. 

“Your brain has to get constructed in some way and these genes we think have something to do with how your brains constructed and how it works, how big it is, all those kinds of things," Elliott said.

Because the brain is responsible for thinking, the researchers linked the brain to intelligence. Through analyzing the GWAS, they were able to determine that brain size is a factor in between genetics and intelligence and that there is a correlation between larger brains and cognitive performance.

Although they already knew that certain genes can predict educational attainment, they were able to better understand “the biological substrate through which those associations would happen,” according to Elliott. 

In this case, it was physical brain size.

This information can help to better understand how genes influence the brain and how the brain then influences one’s overall intelligence, providing better insight to help people achieve. 

Elliott noted that the results from the study can aid researchers in conducting better, genetically-informed studies in the future to determine which environments best lend themselves to fostering intelligence. This could help in finding brain-positive environments that would allow people to reach their potential. 

The paper also compared data from four samples, two of which were convenient samples involving people in and around a college campus and two were population representative samples, which covered a broader spectrum of people. 

"Part of our paper is to try to urge that in neuroscience research and genetic research we’re really making an effort to study population representative samples more and appreciate some of the problems that simply studying convenient samples in and around colleges kind of limits our understanding of some of these things," Elliott said.