Matt Lieberman, a distinguished social psychologist and neuroscientist, basically won the lottery. This past summer, he was offered three million dollars for an academic position—one million in raw income and two to do lab research. That’s a king’s ransom for a psychology professor. On average, psychology professors make less than six figures and rely on a patchwork of modest grants to sustain their research. All Lieberman had to do was spend four months this year and next year in Moscow, a nice enough city, doing some research—which he would have done anyway at home at UCLA.

But there was a catch. He would have to be away from his wife Naomi and seven-year-old son Ian for those eight months. They could not join him in Moscow. He had a basic trade-off problem, one that kept him up for many nights: Should I take the money and give up those eight months with my family or should I stay home and give up the money and research opportunities? In one form or another, we’ve all faced this dilemma, if on a more modest scale. Do you work late tonight or join your family for dinner? Do you go to the conference or to your friend’s wedding? Do you prioritize your career or your relationships?

Lieberman’s new book Social: Why Our Brains Are Wired to Connect hits the shelves this month. It’s a book about relationships and why relationships are a central—though increasingly absent—part of a flourishing life. Lieberman draws on psychology and neuroscience research to confirm what Aristotle asserted long ago in hisPolitics: “Man is by nature a social animal … Anyone who either cannot lead the common life or is so self-sufficient as not to need to, and therefore does not partake of society, is either a beast or a god.”

Just as human beings have a basic need for food and shelter, we also have a basic need to belong to a group and form relationships. The desire to be in a loving relationship, to fit in at school, to join a fraternity or sorority, to avoid rejection and loss, to see your friends do well and be cared for, to share good news with your family, to cheer on your sports team, and to check in on Facebook—these things motivate an incredibly impressive array of our thoughts, actions, and feelings.

Lieberman sees the brain as the center of the social self. Its primary purpose is social thinking. One of the great mysteries of evolutionary science is how and why the human brain got to be so large. Brain size generally increases with body size across the animal kingdom. Elephants have huge brains while mice have tiny ones. But humans are the great exception to this rule. Given the size of our bodies, our brains should be much smaller—but they are by far the largest in the animal kingdom relative to our body size. The question is why.

Scientists have debated this question for a long time, but the research of anthropologist Robin Dunbar is fairly conclusive on this point. Dunbar has found that the strongest predictor of a species’ brain size—specifically, the size of its neocortex, the outermost layer—is the size of its social group. We have big brains in order to socialize. Scientists think the first hominids with brains as large as ours appeared about 600,000-700,000 years ago in Africa. Known as Homo heidelbergensis, they are believed to be the ancestors of Homo sapiens and the Neanderthals. Revealingly, they appear to be the first hominids to have had division of labor (they worked together to hunt), central campsites, and they may have been the first to bury their dead.

One of the most exciting findings to emerge from neuroscience in recent years underlines the brain’s inherently social nature. When neuroscientists monitor what’s going on in someone’s brain, they are typically interested in what happens in it when people are involved in an active task, like doing a math problem or reaching for a ball. But neuroscientists have looked more closely at what the brain does during non-active moments, when we’re chilling out and the brain is at rest. Every time we are not engaged in an active task—like when we take a break between two math problems—the brain falls into a neural configuration called the “default network.” When you have down time, even if it’s just for a second, this brain system comes on automatically.

What’s remarkable about the default network, according to Lieberman’s research, is that it looks almost identical to another brain configuration—the one used for social thinking or “making sense of other people and ourselves,” as he writes: “The default network directs us to think about other people’s minds—their thoughts, feelings, and goals.” Whenever it has a free moment, the human brain has an automatic reflex to go social. Why would the brain, which forms only 2 percent of our body weight but consumes 20 percent of its energy, use its limited resources on social thinking, rather than conserving its energy by relaxing?

“Evolution has made a bet,” Lieberman tells me, “that the best thing for our brain to do in any spare moment is to get ready for what comes next in social terms.”

Evolution only makes bets if there are payoffs—and when it comes to being social, there are many benefits. Having strong social bonds is as good for you as quitting smoking. Connecting with other people, even in the most basic ways, also makes you happier—especially when you know they need your help.

One study of adults found that the brain’s reward center, which turns on when people feel pleasure, was more active when people gave $10 to charity than when they received $10. In another study, comforting someone in distress activated the reward center in a powerful way. Couples were brought into the lab and the girlfriend was placed inside a brain scanner while the boyfriend sat in a chair right next to her. In some cases, the boyfriend would receive a painful electrical shock.

The girlfriend, who knew when her boyfriend was being shocked, was instructed to either hold her boyfriend’s hand or to hold onto a small ball. When the scientists looked at the girlfriend’s brain activity, they found that her reward system was active when she was holding the hand of her boyfriend both when he was being shocked and when he wasn’t in pain—but it was most active when she held his hand as he was being shocked. Holding your boyfriend’s hand feels nice, but it’s especially meaningful when you know that he needs your love and affection.

***

When economists put a price tag on our relationships, we get a concrete sense of just how valuable our social connections are—and how devastating it is when they are broken. If you volunteer at least once a week, the increase to your happiness is like moving from a yearly income of $20,000 to $75,000. If you have a friend that you see on most days, it’s like earning $100,000 more each year. Simply seeing your neighbors on a regular basis gets you $60,000 a year more. On the other hand, when you break a critical social tie—here, in the case of getting divorced—it’s like suffering a $90,000 per year decrease in your income.

You don’t have to be a social scientist to know how badly a breakup hurts. One of Lieberman’s most provocative studies, done in collaboration with his wife Naomi Eisenberg and then-graduate student Johanna Jarcho, shows that social loss and rejection are more painful than we might realize. The researchers put people in a brain scanner and then had them play an internet video game called Cyberball where three people toss a ball around to each other. The research subjects were led to believe that the other people in the game were also part of the study when in fact they were just two pre-programmed avatars.

The point of Cyberball is to make the player (the research subject) feel rejected. At first, all three players toss the ball to each other in turn. But at a certain point, the avatars cut the poor research participant out of the game. They toss the ball just to each other. Even though this is a silly game in a research study and has no bearing on real life, the research subjects were really hurt. They started feeling distress. They felt rejected. When they came out of the scanner, they kept talking to the researchers about how upset they were.

The most interesting part of the study is how their brains processed the social rejection. To the brain, social pain feels a lot like physical pain—a broken heart can feel like a broken leg, as Lieberman puts it in his book. The more rejected the participant said he or she felt, the more activity there was in the part of the brain that processes the distress of physical pain.

In a follow-up study, participants were called into the lab and, like last time, played Cyberball in the brain scanner. But this time, there was a twist. Before they came into the lab, half of them had taken Tylenol every day for three weeks while the other half had taken a placebo. What the researchers found in this study was remarkable: the placebo group felt just as rejected and pained as those in the initial study, but the people in the Tylenol group were totally immune to the social pain of feeling left out.

These studies are no doubt provocative and counter-intuitive. A broken leg and a broken heart seem like very different forms of pain. But there are evolutionary reasons why our brains process social pain the way they process physical pain. Pain is a sign that something is wrong. Social pain signals that we are all alone—that we are vulnerable—and need to either form new connections or rekindle old ones to protect ourselves against the many threats that are out there.

The psychologist Robert Seyfarth has extensively studied female baboons in the field and he finds that they respond to social loss, like the death of a loved one, by making new friends, often through grooming. In humans, too, social pain can be relieved through forming attachments. A baby’s distress cry, for example, calls the mother to reunite with the child and tend to its needs. In studies of rats and their pups, when mothers do not respond to the distress call, the pups often die within two days of birth.

***

Social connections are as important to our survival and flourishing as the need for food, safety, and shelter. But over the last fifty years, while society has been growing more and more prosperous and individualistic, our social connections have been dissolving. We volunteer less. We entertain guests at our homes less. We are getting married less. We are having fewer children. And we have fewer and fewer close friends with whom we’d share the intimate details of our lives. We are increasingly denying our social nature, and paying a price for it. Over the same period of time that social isolation has increased, our levels of happiness have gone down, while rates of suicide and depression have multiplied.

“To be kept in solitude is to be kept in pain,” writes the sociobiologist E. O. Wilson, “and put on the road to madness. A person’s membership in his group—his tribe—is a large part of his identity.”

Across the board, people are increasingly sacrificing their personal relationships for the pursuit of wealth. The American Freshman survey has been tracking the values of college students since the mid-1960s. The survey is a good barometer of social and cultural change and it shows how far we’ve come in prioritizing material values over social ones. In 1965, college freshman said that “starting a family” and “helping others” were more important life goals than being “very well off financially.” By the eighties, it was the reverse: “helping others” and “starting a family” were less important to college freshman than making a lot of money. In 2012, freshmen prioritizing being “very well-off financially” peaked at 81 percent, the highest that number has been in the survey’s history.

“My gut says making more money will make me happier,” Lieberman writes in the book, “but my gut is wrong … The more individuals endorse materialism as a positive life value, the less happy they are with their lives.”

These facts and more were on Lieberman’s mind as he was struggling over the big decision he had to make. After a gut-wrenching couple of weeks and many sleepless nights, Lieberman finally made up his mind. In the end, he turned the three million dollars down. He did not want to be away from his wife and son. “Those are eight months with them,” he told me on the phone, “that I would never get back.” As tempted as he was by the money, he decided that his relationships were more important.

Emily Esfahani Smith is a writer based in New York. She is an editor at The New Criterion, the managing editor of the Hoover Institution’s Defining Ideas, and the editor of Acculturated.

This originally appeared at The Atlantic. More from our sister site:

Here’s why marriage makes our children richer

Why Iceland believes in invisible elves

Why do good athletes have bad teeth?