Homosociality

Homosociality is a term used in sociology, which describes a same-sex relationship which is not romantic or sexual in nature. These relationships might be called friendships, mentorships, or other. Heterosociality is the opposite. It means that one prefers socializing with members of the opposite sex without bringing romance or sex into the relationship. Eve Sedgwick made the term popular in her discussion of male homosocial desire, but Jean Lipman-Blumen had defined homosociality in 1976 as a preference for members of one's own sex.
For example, a close relationship between two men (such as George and Lennie in Of Mice and Men (and indeed most of the characters in that book) would be a homosocial relationship. It can apply to single sex schools, prisons, monasteries, but also to simple friendships.
The relationship can be a sexual one, but a homosocial relationship can occur between homosexuals, heterosexuals or both.
It is often used to describe the all-male world of medieval knights, or sailors. While it can apply to both men or women, it is most commonly used to refer to men.
Evidence
Rose surveyed males and females between the ages of 20 and 28. Rose asked men and women about how they felt about same and cross-sex friendships. Both men and women preferred same sex friendships. Both men and women said that cross-sex relationships were less helpful, and less loyal than same-sex friendships. Friendship formation was found to be different between cross-sex and same-sex relationships as well.
Depending on the culture, and family and social stuctures, same-sex preferences have been found to develop between 3 and 9 years old. (LaFreniere, Strayer,& Gauthier, 1984; Jacklin& Maccoby, 1978; Harkness & Super, 1985) LaFreniere, Strayer, and Gauthier (1984) conducted a three year long study observing fifteen peer groups between the ages of 1 to 6 years old, with 98 boys and 93 girls. As they looked into sex-segregation in childhood, the researchers found that segregation rose with age and that most Western children exihibit these preferences around 3-4 years old. However, in a study by Harkenss and Super, Kenyan children do not have sex-preference in playmates until the ages of 6 to 9 years old. Researchers observed 152 Kenyan children in rural settings and found that this change didn't occur until parental expectations and customary duties increased. "Just when and how such gender segration appears, is the joint product of the individual and the culturally constructed niche" (Harkness & Super, 1985).
The social bias towards members of one's own sex can develop early in children. Specifically, studies have found that by the early age of 3 or 4, children prefer members of their own sex to members of the opposite sex (Bussey & Bandura, 1992). That is, young girls favor other females (girls and women) over males (boys and men). The findings are identical for young boys. Also, Carol Martin (1989) found that boys 4.5 years of age expressed significantly more dislike for a girl depicted as a "tomboy" than a boy depicted as a "sissy"; whereas boys 8.5 years of age express more dislike for a boy depicted as a "sissy". This age difference suggests that children as young as 4 prefer their own sex regardless of gender-incongruent behavior. Around the age of 8 however, boys begin to show males--devaluing feminine behavior. It has also been shown that children ages 10-12 prefer same-sex socializing. That is, girls favored girls who socialized with other girls and boys liked boys who socialized with other boys.
Sexual orientation
Homosociality, by definition, implies neither heterosexuality nor homosexuality. For example, a heterosexual male who prefers to socialize with men may be considered a homosocial heterosexual. The term is often used by feminists to emphasize aspects of solidarity between males. Feminists also identify a close link between female homosociality, feminism and lesbian desire, with Audre Lorde stating "the true feminist deals out of a lesbian consciousness whether or not she ever sleeps with women."
Further reading
Between Men: English Literature and Male Homosocial Desire by E. K. Sedgwick
References
Sociology