The short answer is that we are biologically attracted to those who meet certain criteria that makes them suitable for mating. Studies have shown that people are initially attracted because of the physical appearance and chemical output of those who are good genetic matches for us. In addition, each individual has certain social comparison standards that can be influenced by our exposure to more or less attractive persons in the time period before encountering a potential mate. People also tend to be attracted to those who are similar to them in appearance. Once the physical attraction hurdle has been overcome, the next criteria we use to make a choice of partner is how likeable a person is. Those with warmth who seem to have positive personality traits can become more attractive to us even if they are not up to our standards physically. Another factor that plays into likeability is similarity in attitude and belief. The more someone is like you, the more you tend to like them. This is not always the case, of course because in some instances opposites do attract. There is little data that can explain this phenomenon, however and it tends to be the exception to the rule. In any case, as the feeling of affection influenced by likeability grows, physical attractiveness can increase. As a relationship continues, the feeling of attraction can increase if there are rewards associated with additional encounters with the person. The concept of love is often confused with that of passion and infatuation, which can lead to many unhappy circumstances. Love as we know it is a combination of several factors including: Intimacy (liking), compassion (liking combined with commitment,) and romantic love (liking combined with passion.) Romantic and enduring love is a complex phenomenon which is difficult to define, measure and truly understand. There are, however studies that have been conducted in this area.