It's still a remarkable observation. Presumably urination was a private thing then as it is now. It seems like a coin toss between some 'shaman' suggesting

It's still a remarkable observation. Presumably urination was a private thing then as it is now. It seems like a coin toss between some 'shaman' suggesting it and it turned out to be true vs the many observations that had to happen. Women generally have a good idea, perhaps some women started to observe it as they maybe didn't want more children and didn't want men to know about it and we worried about each and every possible indication that could reveal it.