Science-fiction writers make the best seers. In the late 1950s far-sighted Isaac Asimov imagined a sunny planet called Solaria, on which a scant 20,000 humans dwelt on far-flung estates and visited one another only virtually, by materializing as “trimensional images”—avatars, in other words. “They live completely apart,” a helpful robot explained to a visiting earthling, “and never see one another except under the most extraordinary circumstances.”

We have not, of course, turned into Solarians here on earth, strictly limiting our numbers and shunning our fellow humans in revulsion. Yet it’s hard not to see some Solarian parallels in modern life. Since Asimov wrote The Naked Sun, Americans have been engaged in wholesale flight from one another, decamping for suburbs and Sunbelt, splintering into ever smaller households, and conducting more and more of their relationships online, where avatars flourish. The churn rate of domestic relations is especially remarkable, and has rendered family life in the United States uniquely unstable. “No other comparable nation,” the sociologist Andrew J. Cherlin observes, “has such a high level of multiple marital and cohabiting unions.”

Oceans of ink have been spilled on these developments, yet hardly any attention is paid to the one institution—friendship—that could pick up some of the interpersonal slack. But while sizzling eros hogs the spotlight these days—sex sells, after all—too many of us overlook philia, the slower-burning and longer-lasting complement. That’s ironic, because today “friends” are everywhere in our culture—the average Facebook user has 130—and friendship, of a diluted kind, is our most characteristic relationship: voluntary, flexible, a “lite” alternative to the caloric meshugaas of family life.

But in restricting ourselves to the thin gruel of modern friendships, we miss out on the more nourishing fare that deeper ones have to offer. Aristotle, who saw friendship as essential to human flourishing, shrewdly observed that it comes in three distinct flavors: those based on usefulness (contacts), on pleasure (drinking buddies), and on a shared pursuit of virtue—the highest form of all. True friends, he contended, are simply drawn to the goodness in one another, goodness that today we might define in terms of common passions and sensibilities.

The genius of friendship rests firmly on its limitations. Think of it as the moderate passion.

It’s possible that Aristotle took all this too seriously, but today the pendulum has swung in the opposite direction, and in our culture we take friendship—a state of strong mutual affection in which sex or kinship isn’t primary—far too lightly. We’re good at currying contacts and we may have lots of pals, but by falling short on Aristotle’s third and most important category of friendship, we’ve left a hole in our lives. Now that family life is in turmoil, reinvigorating our notion of friendship—to mean something more than mere familiarity—could help fill some of the void left by disintegrating household arrangements and social connections frayed by the stubborn individualism of our times.

Friendship is uniquely suited to fill this void because, unlike matrimony or parenthood, it’s available to everyone, offering concord and even intimacy without aspiring to be all-consuming. Friends do things for us that hardly anybody else can, yet ask nothing more than friendship in return (though this can be a steep price if we take friendship as seriously as we should). The genius of friendship rests firmly on its limitations, which are better understood as boundaries. Think of it as the moderate passion—constrained, yet also critical. If friendship, as hardheaded Lord Byron would have it, really is “love without his wings,” we can all be grateful for its earthbound nature.

But we live now in a climate in which friends appear dispensable. While most of us wouldn’t last long outside the intricate web of interdependence that supplies all our physical needs—imagine no electricity, money, or sewers—we’ve come to demand of ourselves truly radical levels of emotional self-sufficiency. In America today, half of adults are unmarried, and more than a quarter live alone. As Robert Putnam showed in his 2000 bookBowling Alone,civic involvement and private associations were on the wane at the end of the 20th century. Several years later, social scientists made headlines with a survey showing that Americans had a third fewer nonfamily confidants than two decades earlier. A quarter of us had no such confidants at all.

In a separate study, Nicholas Christakis and James Fowler, authors of Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives (2009), surveyed more than 3,000 randomly chosen Americans and found they had an average of four “close social contacts” with whom they could discuss important matters or spend free time. But only half of these contacts were solely friends; the rest were a variety of others, including spouses and children.

Here, as on so many fronts, we often buy what we need. The affluent commonly hire confidants in the form of talk therapists, with whom they may maintain enduring (if remunerated) relationships conducted on a first-name basis. The number of household pets has exploded throughout the Western world, suggesting that not just dogs but cats, rats, and parakeets are often people’s best friends. John Cacioppo, a University of Chicago psychologist who studies loneliness, says he’s convinced that more Americans are lonely—not because we have fewer social contacts, but because the ones we have are more harried and less meaningful.

Developing meaningful friendships—having the kind of people in your life who were once known as “intimates”—takes time, but too many of us are locked in what social critic Barbara Ehrenreich has called “the cult of conspicuous busyness,” from which we seem to derive status and a certain perverse comfort even as it alienates us from one another. Throw in two careers and some kids, and something’s got to give. The poet Kenneth Koch, whose friends included the brilliant but childless John Ashbery and Frank O’Hara, laid out the problem in verse:

You want a social life, with friends. A passionate love life and as well To work hard every day. What’s true Is of these three you may have two.

If time is a problem, so is space. Although Americans have been relocating less often lately, perhaps as a result of the recession, we still move around quite a bit—for work, sunshine, retirement, or to be near family—and this process of uprooting dissolves friendships and discourages those that haven’t yet formed. Few of us would turn down a tempting new job in a far-off city to stay near friends, possibly for the sensible reason that those friends might move away six months later anyway.

Divorce also takes its toll; most of us over the age of 30 are familiar with the social consequences that ripple outward from a split-up, as foursomes for dinner or bridge are destroyed and friends may find themselves having to pick sides. Marital dissolution usually costs each spouse some precious connections, including in-laws who might once have been important friends.

Our longstanding reverence for self-sufficiency hasn’t helped matters. Ralph Waldo Emerson gave us a sharp shove down this road with his famous essay “Self-Reliance,” and Cole Porter lyricized the uniquely American claustrophobia that danced off the tongues of a parade of popular crooners: “Let me be by myself in the evenin’ breeze/And listen to the murmur of the cottonwood trees/Send me off forever but I ask you please/Don’t fence me in.” Frontier-oriented American mythology is studded with exemplars of the lone hero, from Daniel Boone to Amelia Earhart, to say nothing of the protagonists of Hollywood westerns such as High Noon (1952). Male buddy films date back to Laurel and Hardy, but their profusion in the past three decades—including box-office franchises ranging from Beverly Hills Cop to Harold & Kumar—is a strong social contra-indicator, like the lavish outfits and interiors of movies made during the Great Depression. If something desirable is missing in life, people like to see it on the screen.

Friendship has also suffered from the remorseless eroticization of human relations that was bequeathed to us by Sigmund Freud. The culture stands particularly ready to sexualize men’s friendships since the gay liberation movement mercifully swept away taboos against discussing same-sex relationships. In 2005 The New York Times laid claim to coining the term “man date” in a story—under a woman’s byline—about the anxiety two straight men supposedly experience if they brave a restaurant or museum together and run the risk that people will think they are gay. The “bromance” theme, once strictly a collegiate sport among scholars scouring the letters of passionate 19th-century friends for signs of physical intimacy, has since made its way into popular culture. The pathetic state of male friendship—and the general suspicion that men who seek close friends might be looking for something more—was captured in last year’s filmI Love You, Man,in which a guy decides to get married, realizes he has no one to be his best man, and must embark on a series of “man dates” to find one.

The irony is that straight men could learn a thing or two from their gay brethren, as Andrew Sullivan implied in his insightful book on the AIDS crisis, Love Undetectable: Notes on Friendship, Sex, and Survival (1998). Often estranged from their natural families and barred from forming legally acknowledged new ones of their own, gay men, Sullivan observed, learned to rely not on the kindness of strangers but the loyalty of friends: “Insofar as friendship was an incalculable strength of homosexuals during the calamity of AIDS, it merely showed, I think, how great a loss is our culture’s general underestimation of this central human virtue.”

We make this mistake in part because we’ve allowed our wildly inflated view of matrimony to subsume much of the territory once occupied by friendship. Your BFF nowadays—at least until the divorce—is supposed to be your spouse, a plausible idea in this age of assortative mating, except that spouses and friends fill different needs, and cultivating some close extramarital friendships might even take some of the pressure off at home. Yet the married men I know seem overwhelmingly dependent on their wives for emotional connection, even as their wives take pleasure in friends to whom they don’t happen to be wed. The Beatles’ immortal lonely heart Eleanor Rigby and novelist Anita Brookner’s socially isolated heroines notwithstanding, the fact is that all the women I know are better at friendships—spend more time on them, take more pleasure in them, and value them more highly—than any of the straight men.

Forgive me, guys, but we are lousy at this, and while it may seem to us that our casual approach is perfectly normal, in fact it’s odd. Among people whose lives are more like those of our ancestors, for example, friendship is taken far more seriously. In some cultures, close friends pledge themselves to one another in bonding rituals that involve the spilling of blood. The Bangwa people in Cameroon traditionally considered friendship so important that many families assigned a best friend to a newborn right along with a spouse.

“Friends do not live in harmony,” Henry David Thoreau said, “but in melody.”

There was a time when platonic friendship was exalted—if not idealized—in the West, perhaps in part because of religious paranoia about sex. The myth of Damon and Pythias and the biblical story of David and Jonathan resonated across the centuries, and in the Middle Ages knights bound themselves in ceremonies to comrades in arms. Cicero, Johann Wolfgang von Goethe, Sir Francis Bacon, Michel de Montaigne, William Wordsworth—the list of Western luminaries who have waxed rhapsodic over friendship is long enough to fill anthologies from both Norton and Oxford.

In the 19th century, friendship was the subject of panegyrics by the likes of Emerson, who wrote that “the moment we indulge our affections, the earth is metamorphosed: there is no winter and no night: all tragedies, all ennuies vanish.” His buddy Henry David Thoreau, lamenting that to most people a friend is simply someone who is not an enemy, declared, perhaps wishfully, “Friends do not live in harmony, merely, as some say, but in melody.” Mary Wollstonecraft might have spoken for the lot when she noted that while eros is transient, “the most holy bond of society is friendship.”

A grain of salt is in order: Friendship, like baseball, always seems to send intellectuals off the deep end. Yet there is more biological justification for our predecessors’ paeans to friendship than for our modern-day tepidity. Friendship exists in all the world’s cultures, likely as a result of natural selection. People have always needed allies to help out in times of trouble, raise their status, and join with them against their enemies. It doesn’t seem much of a stretch to conclude that a talent for making friends would bestow an evolutionary advantage by corralling others into the project of promoting and protecting one’s kids—and thereby ensuring the survival of one’s genes.

If we evolved to make friends, we also evolved to tell them things. Humans have an irrepressible need to divulge, and often friends can tell one another what they can’t tell anyone else, a function that has come in especially handy since the Protestant Reformation put so many beyond the reach of the confessional. Less grandly, trading gossip is probably one of the main reasons people evolved into such friend makers, since information (and reputation) have always been valuable—even in the evolutionary environment.

Alliances and inside dope are two of the ways people derive power from friendships, which is why tyrannies are sometimes so hostile to them. Private affiliations of all kinds are a countervailing force against the great weight of government, but Aristotle reminds us that friendship also maintains the state. Friendships, after all, entail mutual regard, respect for others, a certain amount of agreeableness, and a willingness to rise above the ties of kinship in order to knit society into a web of trust and reciprocation—qualities more likely, in a state, to produce Denmark than Iraq.

Living in a society of friends has many advantages. Friendship can moderate our behavior (unless, like the television mobster Tony Soprano, you happen to choose immoderate friends). Friends help us establish and maintain norms and can tell us if we’re running off the rails when others don’t notice, won’t break the news, or lack the necessary credibility. Both our relatives and our friends, the psychologist Howard Rachlin writes, “are essential mirrors of the patterns of our behavior over long periods—mirrors of our souls. They are the magic ‘mirrors on the wall’ who can tell us whether this drink, this cigarette, this ice-cream sundae, this line of cocaine, is more likely to be part of a new future or an old past.”

Indeed, the influence of friends and associates is profound. Social scientists Christakis and Fowler, working with data from the multidecade Framingham Heart Study, found that if you become obese, the odds increase by 71 percent that your same-sex friend will do likewise—a bigger impact than was measured among siblings. On the other hand, when you become happy, a friend living within a mile has a 25 percent greater chance of becoming happy as well—and even a friend of a friend has a 10 percent greater chance. Encouragingly for those who know a sourpuss or two, misery was not comparably contagious.

Friendship can even prolong our lives. For loneliness, the experts tell us, has to do more with the quality of our relationships than the quantity. And we now know that loneliness is associated with all sorts of problems, including depression, high blood pressure and cholesterol, Alzheimer’s disease, poor diet, drug and alcohol abuse, bulimia, and suicide. Lonely people have a harder time concentrating, are more likely to divorce, and get into more conflicts with neighbors and coworkers.

But of course friends are not vitamins, to be taken in daily doses in hopes of cheating the Grim Reaper. The real reason to prize our friends is that they help us lead good and satisfying lives, enriched by mutual understanding. This special way of knowing one another was once exalted as “sympathy,” and Adam Smith described it as “changing places in fancy.” As Caleb Crain made plain in his excellent book American Sympathy: Men, Friendship, and Literature in the New Nation (2001), the 18th and 19th centuries were the heyday of sympathy, when the fervor of friends was evident in their letters as well as their comportment. Sympathy persisted in popular discourse and was studied as a scientific fact under various guises until, in the 19th century, Charles Darwin came along to replace cooperation with competition in the intellectual armament of the day.

Sympathy’s long-ago advocates were onto something when they reckoned friendship one of life’s highest pleasures, and they felt themselves freer than we do to revel in it. It’s time for us to ease up on friending, rethink our downgrade of ex-lovers to “just” friends, and resist moving far away from everyone we know merely because it rains less elsewhere. In Asimov’s vision, Solaria was a lonely planet that humans settled with the help of robots. People weren’t made to live there.

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Daniel Akst, a contributing editor to The Wilson Quarterly, is the author of We Have Met the Enemy: Self-Control in an Age of Excess, forthcoming in January from Penguin Press.

Photo courtesy of Flickr/Lee Haywood