You're creating a circular argument. Western marriage has been defined as the reproductive union between a man and a woman. But this is unsatisfactory. Many Western marriages do not produce children. Western marriage is therefore better understood as a ritualised union meant to enact notions of 'natural law'.
Western 'natural law', which has its roots in Christianity and antiquity, states that a persons biological sex must necessarily correspond to sexual role and also to cultural gender. This is not a universally shared notion - and cultural gender and sexual role are, in anthropology and sociology, distinct categories from biological sex.
Asia and Africa certanly did have marriage. Much of the pre-modern world simply didn't share Western notions of 'natural law', and in many places, sexuality was much less inhibited. In pre-modern China, for example, whilst Confucian law placed emphasis on the continuation of the family line, as long as a man had children he was free to take as many male lovers as he pleased. In the Sepic region of Papua New Guinea, it is believed that all children are born female. Male children must be made - and this is achieved in various ways, including exclusive homosexuality from puberty to adulthood (the individual may also continue to have homosexual relationships for the rest of his life). Also, among the Gheg speaking Albanians of Northern Albania, an individual who is biologically female may assume a male cultural gender. Among native North Americans, 'the two-spirit people' are men who assume a female cultural gender and marry warriors of the tribe.
It's difficult for alot of us in the West to fathom, because we are taught from a young age what are 'appropriate' behaviours for the respective sexes. To many, any variations of these roles are met with anxiety, disgust, fear or condemnation.
some one knows what they're talking about!!!!