a strong predictor of relationship success. She suggests that chemistry comes and goes, and it's important to actively cultivate it because it can help couples deal with future conflicts. Complementarity theory The model of complementarity explains whether "birds of a feather flock together" or "opposites attract." Studies show that complementary interaction between two partners increases their attractiveness to each other. Complementary partners preferred closer interpersonal relationship. Couples who reported the highest level of loving and harmonious relationship were more dissimilar in dominance than couples who scored lower in relationship quality. Mathes and Moore (1985) found that people were more attracted to peers approximating to their ideal self than to those who did not. Specifically, low self-esteem individuals appeared more likely to desire a complementary relationship than high self-esteem people. We are attracted to people who complement us because this allows us to maintain our preferred style of behavior, and interaction with someone who complements our own behavior likely confers a sense of self-validation and security. Similarity or complementarity Principles of similarity and complementarity seem to be contradictory on the surface. In fact, they agree on the dimension of warmth. Both principles state that friendly people would prefer friendly partners. The importance of similarity and complementarity may depend on the stage of the relationship. Similarity seems to carry considerable weight in initial attraction, while complementarity assumes importance as the relationship develops over time. Markey (2007) found that people would be more satisfied with their relationship if their partners differed from them, at least in terms of dominance, as two dominant persons may experience conflicts while two submissive individuals may have frustration as neither take the initiative. Perception and actual behavior might not be congruent with each other. There were cases that dominant people perceived their partners to be similarly dominant, yet to independent observers, the actual behavior of their partner was submissive, i.e. complementary to them. Why people perceive their romantic partners to be similar to them despite evidence of the contrary remains unclear. Evolutionary theories The evolutionary theory of human interpersonal attraction states that opposite-sex attraction most often occurs when someone has physical features indicating that he or she is very fertile. Considering that one primary purpose of conjugal/romantic relationships is reproduction, it would follow that people invest in partners who appear very fertile, increasing the chance of their genes being passed down to the next generation. Evolutionary theory also