> Then please explain why birth rates throughout human history, when life was vastly more difficult and dangerous than it is now, were so much higher?

One of reasons is because more hands were needed to deal with the difficulty

That’s looking at history through a modern lens.

The reality is, women were not able to control when they got pregnant for almost all of human history. It was just part of life and sex.

They weren’t having children as some kind of decades long plan for the benefit of the group… they just had sex and nature did the rest.