Our concepts “natural” and “unnatural” are taken not from biology, but from Christian theology.
Patriarchy has been the norm in almost all agricultural and industrial societies. It has tenaciously weathered political upheavals, social revolutions, and economic transformations.
There is some universal biological reason why almost all cultures value manhood over womanhood. We do not know what this reason is. There are plenty of theories, none of them convincing.
Every culture has its typical beliefs, norms and values, but these are constant flux.
Unlike the laws of physics, which are free of inconsistencies, every man-made order is packed with internal contradictions, and this process fuels change.
Ever since the French Revolution, people throughout the world have gradually come to see both equality and individual freedom as fundamental values. Yet the two values contradict each other. Equality can be ensured only by curtailing the freedoms of those who are better off. Guaranteeing that every individual will be free to do as he wishes inevitably short-changes equality. The entire political history of the world since 1789 can be seen as a series of attempts to reconcile this contradiction.