Human beings are social animals. So there's nothing new about the fact that we learn and grow through our interactions with others.
But new research out of the U.K. suggests these social interactions leave a physical trace in our brains. Scientists say the study reveals the importance of having rich social experiences early in life.
The new study was done in monkeys. But we share a lot in common with our primate cousins, including relatively large brains compared to other animals.
"There's been quite a debate on why is it that our human brain and the brain of other primates are so enormously big," said Rogier Mars, a neuro-psychologist at the University of Oxford.
One theory is that primates evolved big brains to manage their complex social lives.
"They have to keep track of who's dominant, who's been friendly to you in the past, who you have to be friendly with in order to have access to food, to have a good life really," said Mars.
But Mars and his colleagues were interested in a related question: If large brains enable complex social interactions, could social interactions in turn affect the structure of an individual's brain?
To answer that question they worked with a research facility that housed rhesus macaques for a range of scientific experiments.
Mars says the monkeys were already kept in groups of different sizes.
"Some are singly housed, some have one friend, and some have bigger groups."
The researchers wanted to know if the brains of monkeys in the larger groups were different from the brains of monkeys in the smaller groups. So they did MRI scans of the monkeys' brains, and found that indeed there was a difference.
Two parts of the brain were noticeably larger in monkeys that lived in larger groups.
One of those regions is the temporal cortex. It's a region "that contains areas that are sensitive to facial expressions, to body posture, to emotional expressions, all areas that are involved in processing of social stimuli," said Mars.
The other region is the pre-frontal cortex, which sorts through information and helps us make decisions.
The new study is an important one, says Lisa Barrett, a professor of psychology at Northeastern University in Boston.
"It shows that experience in social groupings can change structural aspects of the brain," said Barrett.
Now, this doesn't come as a total surprise.
In fact, a flurry of recent studies in humans has found a connection between the size of social networks and the size of certain brain structures.
In fact, Barrett herself has shown that people with larger and more complex social networks have larger amygdalas, a part of the brain involved in processing social cues.
"These findings do strongly suggest that people who are exposed to larger and more complex social grouping will develop changes in their brain structures, that will be measurable and have visible effects in terms of emotional processing, and social ability and so on," said Barrett.
And that means, those with fewer social interactions early in life might be at a disadvantage later, says Robin Dunbar, a cultural anthropologist at Oxford University. He says this is an especially big concern today, when so many children spend so much time online, engaging in virtual interactions.
"You don't learn how to handle relationships with other people when you do it online because you can simply pull the plug if they offend you," said Dunbar. "You know you don't have to sweat it out, you don't have to find some sort of social compromise with them in the way that you have to in real life the sandpit, or play pit as it were."
But online interactions may also affect the brain. A recent study showed that parts of the brain that process social cues are larger in people with larger online networks. However, those very same people also had large real life networks. So it is unclear, which kind of social interaction has a greater impact on the brain.