"Water will go to water, youth to youth"

"Men of my age flock together; we are birds of a feather, as the old proverb says; and at our meetings the tale of my acquaintance commonly is --I cannot eat, I cannot drink; the pleasures of youth and love are fled away: there was a good time once, but now that is gone, and life is no longer life." - Plato in the Republic.

It is human nature to develop interpersonal relationships (and attraction) based on similarities, such as demographics, physical appearance, attitudes, interpersonal style, social and cultural background, personality, interests and activities preferences, and communication and social skills. Theodore Newcomb (1961) conducted a study on college roommates and observed that students with similar family backgrounds, academic achievements, attitudes, values, and political views became friends.