Men and women around the world, regardless of culture, form more or less formalised sexual relationships that are primarily aimed at the generation and nurturing of Offspring. The two fundamental reproductive strategies implemented by humans and animals alike are polygamy and monogamy Gribbin, Gribbin, ; Wilson, ; Krebs, Davies, The choice depends on a number of factors, mainly environmental. In the case of polygamy, an individual mates with multiple partners, whereas in monogamy, a male and a female mate for a longer or shorter period that spans either a part of the breeding period the so-called serial monogamy or even the whole life Wilson, It appears that relationships formed by contemporary humans are monogamous.
A more thorough analysis has given grounds for distinguishing the two most characteristic types: short-term relationships and long-term relationships.
According to the World Health Organisation WHO , long-term relationships are formed by partners who remain in close emotional and sexual relations for longer than 12 months Izdebski, Ostrowska, Both forms of relationships give partners specific biological benefits.
This is explained by evolutionary psychology in reference to the concept of reproductive success. While permanent relationships increase the chance for the Offspring to survive in difficult conditions because of determined cooperation between the two parents distribution of parental roles, shared protection of the Offspring against threats, shared provision of food to the Offspring etc. Although short-term relationships are very frequent in various human communities, the majority of studies conducted heretofore have focused on marriages.
Studying such type of heterosexual relationships seems hindered by the prevailing set of values, on the one hand, and the tendency to keep promiscuity and infidelity a secret, on the other Buss, According to Buss , casual sex is a taboo, but at the same time a subject of fascination.
