The early primitive society experienced a long pre-marital era, when productivity was very low and people formed small groups to work and live together. Within the group, there is no restriction on the sex of male and female members. With the slow development of primitive society, various forms of group marriage gradually evolved from the initial unrestricted sexual relationship. In the broad concept of marriage and family, the emergence of group marriage marks the emergence of marriage and family system, which can be divided into three historical forms: group marriage, pairing marriage and monogamy. Engels pointed out in "The Origin of Family, Private Ownership and State": "The group marriage system adapts to the marriage and family system in the uncivilized era, the pairing marriage system adapts to the barbaric era, and the monogamy supplemented by adultery and prostitution adapts to the civilized era."