Is Brain Size Really Related To Intelligence?

By Victoria Simpson on June 19 2020 in Science

Image credit: Talaj/
Image credit: Talaj/
  • IQ tests do not measure disrationalia, which is the inability to think and behave rationally despite being quite smart, but they are still considered a benchmark of intelligence.
  • Part of Einstein's brain was found to be thicker than normal, but it is uncertain if it was naturally this way, or whether all his intellectual activity made it grow.
  • Neanderthals had bigger brains than Homo sapiens, yet we have evolved to continue living on Earth and Neanderthals were lost to extinction about 35,000 to 40,000 years ago

You may have seen them before: babies with heads the size of large bowling balls. They are out there! If these people are in your own family, you know what we’re talking about. People may often wonder where these children’s parents actually shop to find appropriately sized winter hats. 

Members of the general public witnessing these wonders of nature basking in their (big) baby strollers may also ask themselves another common question: hey, is that kid the next Einstein? 

Considering the circumstances, it is a logical thing to ask. Big head, big brain, big ideas: these are all connected, right?

According to reports, certain areas of Einstein’s brain, like the corpus callosum, a section of your brain that stretches from front to back and helps the various regions in your brain work together, really was larger than normal for his age. This was discovered when he died. Some say this is a feature that could have helped Einstein explore his renowned intellect and share it with us. People and animals with smaller brains however, have also been found to have above-average smarts, and not everyone with a big brain is a brainiac. Here is what we do know about brain size and its relation to intelligence.   

Bigger Doesn’t Necessarily Mean Better

You probably know some smart men. They do exist. And you also likely know some rather intelligent women. If we assume that people with a larger brain are naturally smarter than the rest of us however, how do we account for the differences in size that exist naturally between female and male human brains? 

According to Christof Koch writing for Scientific, the human brain reaches its biggest size when people are in their thirties and forties. The average size of a brain from a man of European descent, (apologies for the racially narrow data set), was found in MRIs to be about  1,274 cubic centimeters (cm3). That of a woman of European descent was about 1,131 cm3, on average. 

Can we naturally conclude then that men are destined to be more intelligent than women? Some people would jump at the chance to argue this is the case, but we know it is not. In fact, according to the Christian Science Monitor, women now score above men on global IQ tests. 

Furthermore, if a bigger brain makes you smarter, why would evolution get rid of the most intelligent species?  Neanderthals had bigger brains than Homo sapiens, yet we have evolved to continue living on Earth and Neanderthals were lost to extinction about 35,000 to 40,000 years ago. Clearly size is not all that matters.

MRI Scans

All this being said, MRI scans have also found that total brain volume does have a weak connection with a person’s intelligence. According to Scientific American, how big a person’s brain is accounts for somewhere between 9 and 16% of the differences in general intelligence in any given population.  When certain areas of the brain are larger or thicker in one person than in another, such as the temporal, parietal and frontal regions of the cortex, this has been found to be linked with a modest increase in intelligence.

On average, people with bigger brains are actually slightly smarter than their smaller-brained counterparts. Whether or not simply having a larger brain makes you smarter, however, has not been determined. Perhaps increased thinking can make you develop a larger brain. This is a chicken-and-egg problem that has yet to be solved. 

Complexity of Connections, IQ Gene and Other Certainties

Some things have been discovered as certainties when it comes to the brain and intelligence. It is believed by neuroscientists that people who are of higher intelligence generally have more complex cellular and molecular organization of their neural connections, compared to others. This can be seen when looking at a brain under a microscope. Scientists now say that higher intelligence is correlated with greater frontal lobe volume, and a greater volume of neural cell bodies and synapses rather than the size of someone’s brain. 

Your genetics can also come into play. Variations in the HMGA2 gene have been connected with having a higher IQ. This gene is responsible for coding a protein that helps regulate DNA transcription as well as cell growth. 

Defining Intelligence

One key component to studying the connection, if any, between brain size and intelligence is how we define “intelligence”. In the studies scientists have engaged in, intelligence is generally measured according to an intelligence quotient, or an IQ, test. It is hotly debated however, whether or not IQ tests can really detect all types of intelligence, and if they are accurate, or even moral to conduct. IQ tests are said to miss measuring something called disrationalia, which is the inability to think and behave rationally despite being quite smart. These tests are also not exceptional at measuring creativity. 

There are said to be nine types of intelligence and these included naturalist, musical, logical-mathematical, existential, interpersonal, bodily-kinesthetic, linguistic, and intra-personal intelligence. Can an IQ test really “test” them all, and does our society place an equal value on all types of intelligence? 

Instead of the size of our brain, human intelligence is likely linked to how efficiently various parts of our brain work together, and how each individual implements this strength into their life and environment. How we were raised, the opportunities we were exposed to and what self-image we have, may all also play an important part in developing the intricate web we call "intelligence". 

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