When did marriage begin? Ancient societies were led by myths that arose to show people how to live. . . religious myths. . . they shaped the society they bonded. The idea that humans are a monogamous species is incorrect. Instinctively, we are very much like the chimp. He is about 10% dimorhioc just like we are and genetically closest to us of all the other primates. The males are about 10% larger than the females. The larger the difference, the less monogamous a species! Gorilla males are polyigenous and are much larger. The gibbon males are monogamous and about the same size as the females.
There is no indication marriage goes back more than 5,000 years. Before that, there were various forms of family. It was not even known that the male played any role in pregnancy until about 7,000 years ago.
When it began to be realized that the male played a role, religion began to take on more masculine characteristics. The religions that formed the Egyptian and the Mesopotamian societies found that a balance of both male and female gods brought out the best in men and enabled the structuring of powerful government for the first time. Religions follow a pattern of survival of the fittest and shape human social evolution.
The myth that arose and made the change possible was the precurser to the Adam and Eve myth. It emphasized the pair bonding principle. It was the most influencial myth in all human history. A man was to have only one mate.
The institution is not instinctive, however, and it is necesary for society to impose it and maintian it in order for civilization to survive. When people drift away from it, societies and civciliZations crumble.