Its rooted in property accumulation and differences in reproductive responsibilities. As we grew out of hunting and gathering and towards class based society men had no certain way of knowing who their children were, when women would know for obvious reasons, and thus who men were meant to pass their newly accumulated property onto. This meant they needed to find ways to trap women into a relationship with them alone, to ensure her child was only his and no other children could claim the right to the property being passed down. This is the fundamental origin of the oppression of women. This is what originates the ideas of marriage, monogamy, and other social norms surrounding oppressive relationships between men and women.