Schacter's study of affiliation has suggested that all human beings need the company of others. We are sociable animals and therefore need to have interpersonal relationships. These relationships can range from romantic to casual friendships. However the topic most investigated by psychologists is romantic relationships, as nearly all human beings strive to achieve this relationship. Several theories have been suggested as to why human beings are attracted to others essentially the origins of affiliation. An evolutionary theory would suggest that it is a way of preserving ourselves, as we find safety and comfort in the presence of others. Or that we simply wish to ensure that our genes are passed on in the form of our offspring. Other theories suggest that we are attracted to other human beings simply by factors such as similarity or physical attractiveness. Although that in itself has been suggested to indicate 'good genes' by evolutionary psychologists. How physical attractive someone is, is considered to be one of the first things we notice about a person. If a woman's face is seen to resemble that of a young child she is thought of as attractive. Essentially if she has large eyes a small nose and chin. Men are considered attractive if they possess a square jaw, small eyes and thin lips. As Cunningham suggested that this indicated maturity, Eysenck (2001). The 'halo effect' suggests that we form our total impression of a person from this one outstanding trait. We associate physical beauty with goodness, and physical attraction with beauty. Bringham in 1971 suggested that men and women both agree that physically attractive people are thought of as poised, sociable, interesting, independent, exciting and sexually warm, Eysenck (2001). Also physically attractive children are thought of as better behaved and considered more intelligent. The 'matching hypothesis' though suggests that we do not seek the most physically attractive person. Instead we search for someone who is similar to ourselves in physical attractiveness. We seek this compromise as we have a fear of rejection from someone who more physically attractive than ourselves. In 1966 Walster conducted an experiment in which he found that the hypothesis was disproved. Students were asked to rate partners who had been randomly selected. It was found that students preferred partners who were more physically attractive not someone who matched them, Atkinson (2000). However three years later Walster and Walster repeated the experiment but this time the students met beforehand. This time it was found that there was a greater likeness for similar attractiveness. This was possibly because they had more time to think about the qualities they wanted in a partner, and had had enough time to be able to look past how attractive the person was, Eysenk (2001). The theory that similarly attractive people attract was supported by Murstein's research in 1972, Eysenk (2001). He showed pictures of couples and engaged couples and asked people to judge them in terms of physical attractiveness. He found that there was a tendency for the couples to be rated in terms of similar attractiveness. Similarity in attitude is also another factor that has been suggested as why we are attracted to other human beings. In 1961 Newcomb found that 58% of people who shared similar attitudes and lived together were more likely to develop a friendship, Atkinson (2000). In contrast to 25% likelihood of people who had different attitudes forming a friendship. Therefore it does seem to be an important factor in determining interpersonal attraction. However Bryne in 1968 suggested that attitude similarity had more of an effect on interpersonal attraction when the attitudes themselves were of importance, Eysenk (2001). If a certain attitude were important to an individual it would be the similarity between the two people on this topic that would be of most importance concerning attraction. Bryne did a further laboratory study in 1971, where participants had to complete an attitude questionnaire and then later make judgements about another person about whom attitudes are shown. He found we tend to like those with similar attitudes and tend to dislike those with dissimilar. Similarity seems to be valued very highly in what is attractive about fellow human beings, as similarity in personality is also considered an important factor. In 1958 Winch argued that married couples will be happier if they each have complementary needs, so a domineering husband and submissive wife would be well suited, Eysenk (2001). However most evidence indicates that similarity of personality is important. Burgess and Wallin in 1953 studied 1000 engaged couples with reference to 42 personality traits, Eysenk (2001). Finding there was significant within couple similarity concerning at least 14 of the personality characteristics. However when considering interpersonal attraction individual differences must be considered. As some people attach more significance than others to physical attractiveness, personality and attitude. The evolutionary theory suggests that our behaviour must be adaptive otherwise individuals would not have lived long enough to pass them on to their offspring. Our social behaviour towards relationships has been developed over thousands of years, as it has been the most successful at producing offspring. Males and Females both seek sexual partners who are most likely to produce healthy children. This could explain why physically healthy partners are generally preferred to unhealthy ones. Also men tend to prefer women who are younger than them because younger women are more likely to be fertile. In 1930 Fisher devised a hypothesis entitled the 'runaway process'. Stating that females are initially attracted to the features of a male that have survival value. This is also described as the 'sexy sons' hypothesis, Eysenk (2001). The female looks for a physically attractive male, as firstly their desirable characteristics will be passed on to the son. Therefore his reproductive chances will be enhanced thus the mother's genes are perpetuated. Females it has been suggested also select mates on the basis of non-inherited characteristics, most especially their possession of resources. This is because for women there is a large investment being put it when it comes to having children. Therefore they look for a good investment, which in terms of a partner means having good resources. So he will be able to provide for her and her child. Buss's cross-cultural study in 1989 suggests both men and women follow the same patterns of behaviour as predicted by the evolutionary theory when searching for a partner. Finding that men look for women younger than themselves and women for men older than themselves. This is because younger women are more fertile and older men are more likely to have obtained greater resources. Davis's study in 1990 on the contents of personal advertisements gives further weight to the evolutionary theory. He found women more often than not advertised their physical beauty, whilst men emphasised their wealth or other resources. However the notion that romantic relationships have reproduction as their primary goal does not apply to all romantic relationships. He does not account for homosexual relationships or heterosexual relationships in which there is no intention to have children. There is also the Propinquity Effect, which concerns the attraction of other human beings, we tend to like those we find ourselves near and whom we tend to interact. Kerckhoff reports of the Nashville study in which couples within the area applying for a marriage license had there separate addresses measured in miles apart from each other. 61.6% of couples lived within 20 blocks of each other, Kerckhoff (1956). Festinger, Schacter and Back in 1950 found much the same when studying residents in a new housing project. 41% named their next-door neighbour as their best friend, 2% two doors away and 10% three doors away. The attraction of other human beings is that we need human contact. If we are isolated we become fearful and we find comfort and safety in other people. Physical attractiveness seems to play an important role in what attracts us to a specific person. It seems that we are more likely to associate good values upon a physically attractive person than someone less so. Whilst similarity seems too more important in developing an attraction with someone. Whilst the evolutionary theory can be disproved as it does not apply to homosexual relationships and childless marriages. It does however give explanation to certain types of social behaviour towards relationships. Why men tend to prefer younger women and why women prefer older men. However why one person is attracted to another is always going to be hard to explain, as it is such an individual thing. Atkinson, R.Lal. (2000). Hilgard's introduction to Psychology. London: Harcourt Eysenck, M.W. (2001). Social Psychology. Psychology Press Ltd: Sussex Kerckhoff, A.C. (1956). The meaning of residential Propinquity as a factor in mate selection: Social Forces. 34, No3 pp207. 