The next time you find yourself seated in a roomful of strangers, take a close look at your nearest neighbor. Does he or she resemble you in subtle ways? The answer is most likely yes, according to a recent study published in the July issue of Personality and Social Psychology Bulletin.

Although psychologists have long known that humans tend to associate by race, sex and other broad-brush categories, the latest work is the first to suggest that the impulse runs even to the picayune. “Sometimes we either gravitate toward people or away from them not because of a large prejudice but just because there’s something a little bit more—or less—familiar about them,” says Anne Wilson, a social psychologist at Wilfrid Laurier Univer­sity in Waterloo, Ontario, and a co-author of the study. “Most of these processes are not really conscious.”

Wilson and her colleagues per­formed four consecutive experiments using university students in a variety of settings, including a classroom on the first day of a course and tightly controlled laboratory environments in which subjects waited on couches or completed surveys while sitting at large tables. In every case, people tended to sit closer to someone with a trait they shared—for example, the wearing of glasses, hair length or color. The effect held even after the re­search­­ers ruled out the influence of race and sex.

Wilson says the findings help to explain why pairings and groupings of similar-looking individuals seem so common: they are no accident. “People tend to think that someone who looks a little more like them is more likely to think like them,” she says. “If you expect someone to be more like you, you might behave toward them in a more open and likable way.” And that kind of “social lubrication” is a key ingredient in the foundation of a lasting relationship.