So poligamy, slavery, incest and the like are OK if it helps the nation of Israel grow in numbers?
Different times, different place.
Polygamy- still practiced by outlaw mormons, ask them how well it works, not me. I've seen TV reports where all of them seem to be happy. Just because modern society deems something to be wrong (or right), does not make it so. Admittedly, it's hard to put ourselves in that position. But if we lived in those times, if you really try to put yourself into those times, living as a tribe, in the wilderness, it makes sense and had many advantages.
Slavery- Already covered that, better a live slave than a dead "freeman". We are all slaves, you and I included.
Incest- Looking at these things through modern spectacles, it is hard to see things as they were. Apparently the human genome allowed close mating back then without defects. Even in our day, most states allow first cousins to marry, and there are remarkably few defects as a result. Most domesticated animals are still "line-bred".
Life as a tribe in the wilderness surrounded by opposing tribes who wanted everything you lived for at any cost was a fact of life in those days (OT). Read history on any tribal society, even to our day, and it gives a different perspective to what you might judge as "moral" given our comfy existence in twenty first century western society.
BA
PS- 5go, you are assuming that the onset of menstruation has not changed, I am assuming nothing, simply pointing out that it is unkown what effect thousands of years has had on the onset of menstruation.