Brain Size Alone Tells Us Little About Intelligence — Here’s What We Know
“The bigger the better” seems to be one of those maxims that humankind is hardwired to live by. The notion is followed pretty consistently throughout nature, too, at least when it comes to gathering resources and choosing mates.
But humans possess a particular preoccupation with size, especially at the anatomical level. In the course of our history, we’ve been preoccupied with the sizes of various organs and physical attributes of the human body, often making value judgments between the largest and smallest specimens.
This is especially true — and at times especially problematic — when it comes to one body part that we can’t easily see, but which defines us as modern humans. We’re talking, of course, about the brain.
Does a bigger brain mean you’re smarter? It’s an innocent-enough question, one that scientists have entertained for centuries, but it can also be a loaded one. As we’ll see, historical attempts to study head and brain size have not always yielded conclusive or valid results. Regrettably, this area of scientific inquiry has been tainted by bias over the decades and has led to some pretty sexist and racist leaps of logic.
Current research by modern neurologists, psychologists, and other scholars of the mind and brain has yielded some interesting findings. For one thing, there may indeed be some benefits to having a larger brain. It’s not the full story, though.
“We know now that size really isn’t everything. There are many other factors that may contribute, especially early life environment. There’s an experiential factor in play as well. Good health, better food, access to education — these can all make a difference,” Charles DeCarli, lead author of the study and director of the UC Davis Alzheimer’s Research Center, told Discover.
Bigger Brain, Better Health?
One result of modern neurology research is that human brains are getting bigger overall. And while that size increase may not correlate with higher intelligence, it could indicate better cognitive health.
In a 2024 study published in JAMA Neurology, researchers at the University of California Davis found that participants born in the 1970s had larger brain volume and surface area — as much as 15 percent larger — than those born in the 1930s.
“The decade someone is born appears to impact brain size and potentially long-term brain health,” said Charles DeCarli, lead author of the study and director of the UC Davis Alzheimer’s Research Center, in a news release. Larger brain structures, such as what DeCarli and his co-authors found, “may reflect improved brain development and improved brain health,” DeCarli noted in a news release that accompanied the study.
But even uneducated individuals can score highly in measures of intelligence, and DeCarli’s group is now examining what other factors might be in play.
“A big part of what we’re looking at right now relates to connectivity,” he told Discover. “The more we can understand how various parts of the brain connect with other parts, that may give us better insight.”
Read More: The Brain Sparks Sudden “Aha Moments” As We Try to Decipher Tricky Visual Puzzles
Ancient Views on Brains and Biases
This examination of the brain is an obsession that we’ve held since ancient times: early Egyptians studied human brains to better understand disease and injury, although they believed the heart was where our intelligence resided.
Beginning around the 5th century B.C.E., Greek scientists identified the brain as the seat of intellect and memory, according to a study in the European Journal of Neuroscience. Working with cadavers, the Greeks performed some of the earliest known dissections and systematic descriptions of the human brain. They also inevitably measured brain size, noting how much larger our brains were (at least in proportion to body size) than those of most animals. It was no great leap for these early thinkers to suppose that our much larger brains were just one of the many reasons humans were the dominant species on the planet.
By the 19th century, specialized disciplines emerged that focused on both brain and skull size, leading to questionable inferences and conclusions about human intelligence — not compared to other creatures in the animal kingdom, but to other members of our own species. These areas of research were deeply flawed, susceptible to bias, and would cast a long shadow over the scientific study of brain size.
Craniometry, for example, claimed to use various skull measurements to provide insight into the intellectual capacity and behavioral traits of the brain within. Researchers in the field amassed large collections of human skulls — not always ethically — from people of various races and backgrounds around the world to make “informed” comparisons and hierarchical classifications of different types of humans.
A related area of study, phrenology, purported to provide insight into an individual’s intelligence, as well as their personality traits and overall character, by examining not only head size, but also other features, including contours, bumps, and depressions on people’s skulls.
Both “sciences” enjoyed an unfortunate vogue in the scientific community of the era, which was overwhelmingly white, Christian, and male. Research in these areas was unsurprisingly influenced by the biases of that demographic.
Biases and Darwin’s Descent
Even Charles Darwin, whose theories on evolution still frequently keep him on lists of all-time greatest scientists, went astray with cranial measurements, per EMBO Reports. In his 1871 book, The Descent of Man, and in other works, Darwin maintained that women were stunted and inferior to men, as well as incapable of higher reasoning and emotional control, simply because their skulls and brains were consistently smaller than men’s. He also supported Pierre Paul Broca, who believed Caucasians had bigger brains and, therefore, superior intelligence.
Their adherence to these areas of junk science would be a blot on the reputations of both men, especially since their influence no doubt helped give craniometry and phrenology a longer life and respectability than they ever deserved to have. Although both areas of study would be challenged by most of the scientific community by the 20th century, they continued to have their adherents.
Nowadays, both areas of study are completely discredited by neuroscientists, psychologists, and anthropologists. But research into brain size and cognitive health and function remains a popular area of legitimate, unbiased scientific inquiry.
Brain Size and Intelligence
The bottom line, DeCarli told Discover, is that you can’t just look at size when you’re looking at intelligence. “There are just too many other things to consider. Experience, upbringing, aptitude. These and other factors are going to play roles in someone’s overall intelligence.”
Perhaps there’s no better proof of this than the research surrounding one of the most famous “big brains” in human history — Albert Einstein’s. When Einstein died in 1955, the doctor who conducted his autopsy saved the physicist’s brain before the body was cremated, according to a study in Brain.
After receiving permission from the family to study it, scientists weighed, measured, and examined Einstein’s brain extensively. While they had various inconclusive theories about the special ways this brain might have functioned, one thing was clear: Einstein’s brain was no larger than that of a person with normal intelligence. In fact, it was a little smaller and lighter than average.
So much for bigger being better.
Read More: The Brain Sparks Sudden “Aha Moments” As We Try to Decipher Tricky Visual Puzzles
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