Why our brains are getting smaller

Oct 2, 2023, 2:00 PM

A brain on a white background....

That belief has evolved as we've learned that the human brain has actually shrunk starting approximately 3,000 years ago. This is not a microscopic change. Our grey matter has shrunk about the size of a lime. (Canva)


SALT LAKE CITY — Humans have long believed that our superior intelligence is connected to our brains being larger than other species relative to our body size.

That belief has evolved as we’ve learned that the human brain has actually shrunk starting approximately 3,000 years ago. This is not a microscopic change. Our grey matter has shrunk about the size of a lime.

“It’s important not to conflate brain size with smarts,” explained Dr. Rachna Reddy, a biological anthropologist, primatologist and Assistant Professor of Anthropology at the University of Utah. “Having a larger brain does not equate in any way to more intelligence.”

So, why is our brain shrinking? Reddy commented on the new study from Dartmouth.

“One hypothesis that the authors put forward is that humans have come to rely on collective intelligence,” she said.

What is collective intelligence?

In modern society, we all do so many different things every day. We drive cars, use phones and the internet, eat a variety of food.

“No one person is really capable of knowing all of the skills and possessing all that knowledge,” Reddy said. “So, you use a cellphone every day, but if I asked you how each piece of it worked, there might not be a single person who could put together every piece of the cellphone. That would include finding the minerals necessary to make all the parts, and programming all the parts. These are all specialized skills that come together in a cooperative way to accomplish this one task that allows many different people from all over the world to communicate.”

Our culture is cumulative. We benefit from what is learned generations ago and last month. A big reason for that is that we have language.

“We’re able to share all kinds of information even when we’re not there,” Reddy said.

Ant brains

The authors of this recent study use a comparative approach. They look at other places and species where there is a similar pattern and then infer what might have caused that pattern.

For instance, “They looked at how ant brains have changed over time,” Reddy explained. “Scientists have studied ants and linked aspects of the way they cooperate with each other to the way humans do. There are a lot of key differences, of course.”

“Ants are eusocial insects,” she continued. “They work as a group in order to survive. They travel great distances and accomplish many things by working together, as humans do. So maybe there are some sort of parallels from which we can make inferences.”

Dr. Reddy studies chimpanzees, human’s closest living relatives. “They do a lot of things cooperatively,” Dr. Reddy said. “They hunt together, sleep near each other. But chimps don’t have language. They can’t share information over time in a cumulative way like we do. They can’t pass knowledge down.”

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Why our brains are getting smaller