Similarity/attraction theory posits that people like and are attracted to others who are similar, rather than dissimilar, to themselves; "birds of a feather," the adage goes, "flock together." Social scientific research has provided considerable support for tenets of the theory since the mid-1900s. Researchers from a variety of fields such as marketing, political science, social psychology, and sociology have contributed to and gleaned information from empirical tests of similarity/attraction theory. The theory provides a parsimonious explanatory and predictive framework for examining how and why people are attracted to and influenced by others in their social worlds.
A large body of research investigates the role that similarity of attitudes plays in attraction. According to studies by Ellen Berscheid and Elaine H. Walster (1969) and Donn Byrne (1971) in general people are most attracted to others who share similar attitudes. Additionally people who share similar important attitudes (e.g., attitudes concerning home and family) are more likely to be attracted to each other than those who share less important attitudes (e.g., attitudes toward certain fabric softeners).
There are several reasons why people prefer the company of others who espouse attitudes, especially important attitudes, which are similar to their own (Berscheid and Walster 1969; Byrne 1971). Most importantly perhaps, sharing similar attitudes provides corroboration that a person is not alone in his or her belief; they might even be correct to hold the attitude in question. Other possible reasons suggested for why people prefer others who are similar to themselves are that (1) knowledge of similar attitudes may help people to predict others’ future behaviors, providing a predictive "window" into the other’s behavioral predilections, and (2) people may be more likely to assume that others who hold similar attitudes to themselves have a greater chance of being attracted to them, a "likeness begets liking" explanation.
In addition to people’s inclinations to be attracted to those who share similar attitudes, people are also attracted to others who manifest personality characteristics (e.g., optimism, self-esteem, shyness, conscientiousness) that are similar to their own. In fact people may choose to associate with certain others because they have similar personalities. For example friends are more likely to share personality traits than nonfriends. Moreover, marital partners share more similar personalities than people in randomly assigned pairs. Indeed personality similarity may play a key role in marital happiness and longevity (Berscheid and Walster 1969; Byrne 1971).
Furthermore people are attracted to romantic partners who share similar physical characteristics and levels of physical attractiveness. Tall people are more likely to marry tall partners than short ones, and attractive people are more likely to marry attractive partners than unattractive ones.
People’s preference for similarity in social partners is not limited to the aforementioned domains, though. Research has demonstrated that people report greater liking for and attraction to people who are like them in the following areas as well: socioeconomic status, religious beliefs, social habits (e.g., frequency of attending parties), bad habits (e.g., drinking and smoking), ethnicity, and intelligence.
Similarity/attraction theory may not hold in all social instances, however. For example some scholars have suggested that people may be more likely to be attracted to partners who complement rather than replicate certain attributes. This complementarity view of attraction explains, for example, why attractive younger women may form successful marital unions with much older, wealthier men. Along similar lines people may not like others who share negative personality traits with them. Rather than be constantly reminded of their faults in a given dimension through the presence of someone similar, people may prefer to interact with others who they believe will "bring out the best" in them.
Additionally some researchers, such as Milton Rosenbaum in a 1986 study, have suggested that attitudinal dissimilarity, rather than attitudinal similarity, drives the similarity-liking link. According to the dissimilarity-repulsion view people’s motivation to avoid social interactions with dissimilar others is stronger than, or at least as strong as, people’s desire to affiliate with like-minded others. Indeed a 2000 study by Ramadhar Singh and Soo Yan Ho revealed that, under certain circumstances, the influence of attitudinal similarity and dissimilarity may exert equivalent and opposite effects on liking. Further in some cases, dissimilar attitudes may have a stronger influence on interpersonal attraction than similar attitudes (Singh and Ho 2000).
In summary similarity-attraction theory attempts to explain and predict interpersonal liking by asserting that people are attracted to others who are similar to themselves. Consistent with this view, research has revealed that people prefer to affiliate with those who share similar attitudes, personalities, physical attributes, and a host of other characteristics compared to others who do not. Though similarity/attraction theory explains many cases of interpersonal attraction, it may not accurately predict all attraction outcomes. In some cases complementarity or avoidance of dissimilar others may better explain certain patterns of human liking.