For much of human history, these immediate social networks took the form of multi-generational communities that were rooted in shared geography, expressed through the intimacy of kinship, shared religious beliefs, rituals, practices, and values, and were nourished by working and living in the same environments and experiencing similar things. But in densely packed cities, most individuals’ extended social networks take the form of complex intersecting mosaics of relationships cobbled together from our involvement in a whole series of sometimes very different interests and hobbies. And, perhaps unsurprisingly, for many of us our regular social networks are made up of people we have worked with or encountered at work.

In the mid-1970s, a Harvard sociologist named Mark Granovetter published what became the landmark study of how people get jobs. What he found and others have confirmed, is still true today: Most people find their jobs through personal connections. What surprised Granovetter—and hence the name of his famous “strength of weak ties” study—was that those personal contacts were neither friends, family, nor close work associates.

In a study reported in the MIT Sloan Management Review, more than 200 executives were asked to reconnect with such people and to use their interactions to get information or advice that might help them on an important work project. The executives reported that the advice they received from these dormant sources was, on average, more valuable and novel than what they obtained from their more active relationships. In fact, many of the “weak ties” activated by Granovetter’s job hunters were connections developed earlier in their careers that had been dormant.

All of these studies, as well as our own Harvard Study, bear witness to the importance of human connections. They show that people who are more connected to family, to friends, and to community, are happier and physically healthier than people who are less well connected. People who are more isolated than they want to be find their health declining sooner than people who feel connected to others. Lonely people also live shorter lives. Sadly, this sense of disconnection from others is growing across the world. About one in four Americans report feeling lonely—more than sixty million people. In China, loneliness among older adults has markedly increased in recent years, and Great Britain has appointed a minister of loneliness to address what has become a major public health challenge.

This analysis echoes the findings of the study highlighted in the article in Science: across all age groups, genders, and ethnicities, strong social connections were associated with increased odds of living longer. In fact, Holt-Lunstad and her colleagues quantified the association: incredibly, social connection increased the likelihood of surviving in any given year by more than 50 percent. Across all of these studies, the mortality rate of individuals with the fewest ties was between 2.3 (men) and 2.8 (women) times higher than that of individuals with the most ties. These are very large associations, comparable to the effect of smoking on getting cancer. And smoking, in the United States, is considered the leading cause of preventable death.