There are four factors that underlie interpersonal attraction: physical attractiveness, similarity in personality between the two people, geographical location and the amount of self-disclosure presented. Scientists have had a difficult time studying interpersonal attraction because the behavior itself has to be replicated in a lab, which uses artificial conditions.
These artificial conditions make it impossible to study the behavior naturally and so it can be difficult to draw conclusions based on studies. These research studies also tend to have disproportionate amounts of middle class, white college students in them, as well as having only people of western cultures. Furthermore, these people have not seen one another before the study and are unlikely to see one another after the study.
When studied, geographical nearness has been a factor in attraction because this is how people are able to meet one another in the most natural sense. Running into someone who lives in the same city is more likely than running into someone who lives 3,000 miles away. Another factor, physical attractiveness, is hardwired into a person's chemical makeup. Numerous studies have shown that physical attractiveness increases the desire for people to interact because people prefer to have physically attractive mates and friends. People who are physically attractive are considered to be happier, healthier, more successful, more socially skilled and more sensitive. However, the idea of physical attraction is subjective and also varies by culture.
People who are able to self-disclose details about themselves without over-sharing often cement themselves in the mind of their new acquaintance as a genuine person, which is typically thought to be more attractive. The final factor is how similar the two people are. People are always interested in dating people who share similar interests and in being friends with other like-minded individuals.