First — a bigger brain doesn’t automatically mean higher intelligence. Brain size only weakly correlates with measures of intelligence in humans. Albert Einstein’s brain, for example, was relatively small — and he was Einstein!
In Einstein’s case, researchers point to unusually complex folds (gyrification) in several areas of his brain, which may help explain his abilities. More broadly, modern studies suggest the link between intelligence and overall brain volume in humans is weak or absent.
Is Our Brain Really Shrinking?
Scientists haven’t reached a consensus. Still, many specialists see evidence that average brain volume has decreased over time.
“My research shows that during the Holocene (the epoch after the last Ice Age, from roughly 11,700 years ago to the present) human brain volume decreased by about 10%, or on average by roughly 150 ml,” said Maciek Henneberg, professor emeritus of comparative and anthropological anatomy at the University of Adelaide. In that study, he analyzed skulls from around the world and examined many specimens personally.
Brain researcher Jeff Stibel, who has published several papers on brain shrinkage, points out that warming during the Holocene coincided with more than a 10% reduction in brain size in modern humans. He added data from roughly 800 additional skulls worldwide.
Other studies reach different conclusions. For example, Brian Willmore, an associate professor of anthropology at the University of Nevada, Las Vegas, found no evidence that the human brain changed “in any substantive way” after our modern form appeared.
“We need to be more cautious in drawing conclusions,” says John Hawks, a professor of anthropology at the University of Wisconsin–Madison. He emphasizes that existing datasets often consist mostly of skulls from men of European descent, so it’s hard to make global claims about highly diverse populations.
Why Might Human Brains Be Shrinking?
If brains really have gotten smaller, researchers propose a few possible explanations.
1. The shift to farming and other lifestyle changes
One idea ties the change to the adoption of agriculture. During the Holocene people gradually started producing food — for example through farming and animal husbandry — which allowed them to live in larger communities. The physical strength needed for hunting big animals and defending against predators became less important; a smaller body required less food and therefore had an advantage in natural selection.
Not only did brains get smaller — bodies changed too. At the end of the Ice Age, average male height was about 1.75 m (roughly 5 ft 9 in), while in agricultural communities in the mid-Holocene it averaged about 1.65 m (roughly 5 ft 5 in). Body mass fell even more: bones became thinner and less robust. Meanwhile, average height has increased in some regions recently, and Hawks says that could affect brain size as well.
2. Climate and the Bergmann–Allen rules
Warming after the Ice Age may also play a role. Stibel points to biological principles known as the Bergmann–Allen rules: in warmer climates bodies and organs tend to be smaller so that a relatively larger surface area helps dissipate heat.
3. Specialization, collective intelligence, and division of labor
Another hypothesis links the change to how we think and work together. Population growth and the division of labor led people to specialize and rely on one another: it’s no longer necessary for every person to know everything — it’s enough to have a narrow set of skills needed for society to function.
Have We Gotten Smarter?
Smaller brain size doesn’t automatically mean we’ve become smarter or dumber — it suggests intelligence may have changed in kind.
“We probably traded away some raw computational power in exchange for access to collective intelligence,” Stibel says. “Whether that’s a gain or a loss depends on how you define intelligence, and on how stable the cultural and technological systems we now heavily rely on turn out to be.”
So the answer is both simple and complex: even if some data point to reduced brain volume during the Holocene, that doesn’t contradict increases in some measures of intelligence (for example, IQ in the 20th century). The key difference is that we’ve changed how we use knowledge, how we spread skills, and how much we depend on collective memory networks and technologies — a different quality of cognitive ability that brain volume alone doesn’t capture.
Based on material from Live Science
Photo: Unsplash
