The term for people to associate with others who are similar is "Homophily" ("love of the same"). This idea applies not only to appearance, but to temperament, religion, social status, hobbies, etc. People tend to associate with those who are similar ... and the more similarities, the stronger the bond. It's the scientific way of saying "birds of a feather flock together."
Scroll Down to Read Other Opinions
The only opinion from guys was selected the Most Helpful Opinion, but you can still contribute by sharing an opinion!