No, homophily has nothing to do with sexual orientation. In the 1950s, a pair of sociologists, Paul Lazarsfeld and Robert Merton, coined the term to refer to the pervasive tendency of humans to associate with others like themselves.
Even if you don’t know homophily by name, you have experienced it throughout your life. In whatever elementary school you went to, in any part of the world, girls tended to be friends with girls and boys with boys. If you went to a high school that had people of more than one ethnicity, you saw homophily there. Yes, you may have been friends with someone of another ethnicity, but such friendships are the exception rather than the rule. We see strong homophily by age, ethnicity, language, religion, profession, caste, and income level.
Homophily is not only instinctual (just watch people mingle at any large social event where they’re all strangers) but also makes sense, for many reasons. New parents learn from talking with other new parents and help care for one another’s children. People of the same religion share beliefs, customs, holidays, and norms of behavior. By the very nature of any workplace, you’ll spend most of your day interacting with people in the same profession and often in the same field. Homophily also helps us navigate our networks of connections. If you need to know a doctor’s reputation, which one of your friends would you ask? The one who’s in the healthcare industry, of course, as they would be the most likely to know the doctor or know someone who knows the doctor. Without homophily, you’d have no idea of whom to ask.
As simple and familiar as it is, homophily is very much a scientific concept: It’s measurable and has predictable consequences. In fact, it’s so ubiquitous that it should be thought of as a fundamental scientific concept. But it’s the darker side of homophily that makes it such an important one.
As the world struggles with inequality and immobility, we can debate the importance of the role political regimes or capital accumulation plays, but we miss a primary constraint on upward mobility if we ignore homophily. To understand why many young Americans join gangs and so many end up shot or in jail before their twenty-fifth birthday, we’ve only to look at what they observe and experience from a young age. If we want to know why universities like Stanford, Harvard, and MIT have more than twenty times as many students from the top quarter of the income distribution as from the bottom quarter, homophily is a big part of the answer. High school students in poor neighborhoods often have little idea of the financial aid available or the benefits of higher education, or even what higher education is. By the time they talk to a high school counselor who might have a few answers, it’s much too late. Homophily affects how their parents raise them, the culture they experience, the role models they see, their beliefs, the opportunities coming their way, and ultimately the expectations they have for their lives.
Although we’re all familiar with homophily, thinking of it as a measurable phenomenon may add to the discourse on how to increase upward mobility and decrease inequality around the world. Achieving these goals requires recognizing that persistent segregation by income and ethnicity prevents information and opportunities from reaching those who need them most. Homophily lies at the root of many social and economic problems, and understanding it can help us better address them—from inequality and immobility to political polarization.