Women have control over access to sex. At the same time, men invest heavily in the upbringing of their children, something unique amongst the Great Apes and rare in mammals, with only 5% of species exhibiting it. These are the basis of the social contract that has made humans so successful. Life has only one purpose: to ensure its own continuance.
Understanding how this works and the reasons why women control access to sex is relatively simple. Women need to ensure that the maximum number of their children survive to adulthood. This is not the same as the maximum number they could possibly have. A woman, beginning at the menarch, say age 14 and ending at the menopause, say age 45, could potentially have over 30 babies. But this is vanishingly rare, because in such a large family, many would die. Each child who dies is a huge loss to the woman but also to the community around her. Each represents a huge investment in time and resources that cannot easily be replaced. Simple human cultures cannot survive if they do not attend to this. Yet women are permanently receptive and fertile, whenever they are not pregnant. This means they can always get pregnant, if they do not control men’s access to sex. That control is essential to human species survival and we have developed numerous methods to permit it.