DaVinci brain

Three millennia of civilization have had an impact on many aspects of human life. But one contested area of ​​research is whether changes in civilization have affected the size of our brains.

A study published in 2021 seems to indicate that our brains shrank in the last 3,000 years—about the time when we began to practice agriculture more widely and when complex civilizations began to flourish in many parts of the world. But a new study revisiting this previous work criticizes the way these authors used their data. This recent researchpublished last month in Frontiers in Ecology and Evolutionsuggests that our brains really haven’t shrunk at all over the past three millennia.

“People have this idea that we’re transferring, we’re getting dumber,” said Brian Vilmoare, a biological anthropologist at the University of Nevada, Las Vegas and co-author of the recent study. Part of that perception, he argues, comes from papers like the 2021 paper. “When I looked at the study, I could see some problems in the math,” Vilmoiré says.

Seemingly smaller brains

In the 2021 study, Dartmouth University paleoanthropologist Jeremy DeSilva and colleagues extracted 985 brain sizes from previously published studies that had taken measurements of modern humans and our ancestors. They found that hominin brains increased on average from 2.1 million years ago to about 1.5 million years ago. Then, about 3,000 years ago, our brains began to shrink in size.

The researchers of this paper theorized that the advancement of human civilizations at the time may have been responsible for the reduction in brain size. Around 1500 BC, many people began to live in larger cities, in more densely packed populations. “Because groups make decisions, not individuals, there will be less selection for intelligent individuals,” says Vilmoiré, summarizing the scientists’ thoughts.

What happened to modern humans reflects the same progression that happened in ant societies over time, the scientists speculate. Because labor is divided in ant societies, many of the insects don’t necessarily have to think much, and so have evolved smaller brains. “Ant and human societies are very different and have taken different paths in social evolution,” said paper co-author James Traniello, a biologist at Boston University, in press release. “However, ants also share with humans important aspects of social life, such as group decision-making and division of labor, as well as producing their own food. These similarities can inform us more generally about the factors that may influence changes in human brain size.

Small Brains Reassessed

Still, the results of Desilva’s study did not sit well with Villmoare. He and a colleague decided to take a closer look at the data and found that the researchers had focused too much on data from the last century—more than half of the nearly 1,000 brain sizes they analyzed were from the last 100 years, while only 23 sizes of the brain were drawn from the time frame critical to their hypothesis several millennia earlier.

Beyond that, Vilmoiré and his colleague argue, the data presented by the study’s authors from 2021 suggest random changes rather than a steady decline. And as for the ant comparison, Villmoare says the process of evolutionary selection is very different between humans and ants. It would be more appropriate, he says, to compare humans to other social animals such as elephants. Elephants’ brains are much larger relative to their body size than rhinoceroses, which do not have such complex social structures.

“Social animals tend to be more encephalized,” Villmoare says, referring to an evolutionary increase in brain size relative to body size. Brains typically only shrink over generations in species, he says, when evolutionary pressures force bodies to compensate by adding weight elsewhere. This can be reflected in animals that develop larger muscles, for example in times when food is scarce.

For Villmoare, the problems facing a complex society demand More ▼ thinking, not less thinking because there is more competition around to mate and more complex social alliances to maneuver. “All of this puts enormous demands on the brain.”

What does it all mean?

De Silva welcomes this criticism of his research. “Fifty years of research into the evolution of the human brain has consistently found that modern human brains are smaller than they were in the Pleistocene,” he says. “So when we started our research, we didn’t researchifbrains shrank butwhenthis happens.” The fact that Villmoare’s research suggests that the brains of modern humans have not decreased in size is an “interesting mystery” that he hopes to address in further research.

Villmoare says the disagreement is collegial — he calls DeSilva a friend. But so far he remains unconvinced based on findings that human brains have shrunk at all in the roughly 300,000 years since then Homo sapiens have walked the earth. And even if our brains have shrunk, that doesn’t mean we’re necessarily less intelligent than our ancestors. “Even brain size alone does not necessarily correlate with intelligence,” Vilmoiré says, citing the example of Albert Einstein, whose brain was smaller than average.

Meanwhile, the Neanderthals had larger brains than modern humans, although their gray matter is not necessarily larger in all the same regions as humans. “There’s a lot more going on in the brain than volume,” adds Villmoare.

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