While social customs, culture, and technology are constantly changing, our brains and bodies have been handicapped to the slow pace of evolutionary time. As in they haven’t had time to change in any significant way during the few thousand years since we were all hunters and gatherers, when our only job was survival. Survival means one thing: staying alive long enough to reproduce, so that the next generation can stay alive long enough to reproduce. The way the primal section of our brains are designed, nothing else matters besides survival.
A few hundred million years ago, a creature came along and thrived, because instead of eating its young, it cared for them. Some of the earliest ones laid eggs, and had a pouch for carrying the infanst and nipples for feeding them. These evolved into creatures that, instead of laying eggs, gave birth to live young and took care of them until they had developed relative independence. But in order to have those kinds of interactions required a more complex brain. A new layer of brain material developed controlling emotional responses called the limbic system. As these new creatures, called mammals, evolved further, the limbic system grew in size and complexity. The limbic system allowed the ability to learn new responses, as well as hold a complex memory that allowed learning. But the most remarkable ability the limbic system gave these creatures was the ability to assess the internal state of another animal. Mammals and reptiles both make noises through which they can transmit information, but mammals are capable of a much richer variety of language, creating a drastically different means of communicating.
When your brain was fashioned by natural selection, the first man who impregnated a woman had a good chance of dominating her reproductive years. Some thousands of years ago, women were either pregnant or nursing almost continuously from puberty until death at a young age. Since nursing inhibits ovulation, this reduced the chances of becoming pregnant. The reason men of any age continue to find youthful qualities attractive in females is that they were designed to get them pregnant and dominate their fertile years by keeping them that way. In many cultures, it’s perfectly acceptable for a man to take a second wife, who is usually younger. In our culture, its considered taboo, yet the advertisements for it are everywhere. Only our opinions about this process has changed, not our innate machinery.