I'm not sure what relation to being monogamous this has but you are right.
If women only had one child in their lifetime and human numbers would dwindle until we didn't exist. Even if we had a perfect 50/50 split, it would still end up getting down to there being one individual left who would have no mating partner.

A + A = B
A + A = B
B + B = C

But now you need an extra 2 generations of A to make one of B to make another one for C to mate with. We would become extinct if this were the case.

If mass polygamy were common, and a guy had a harem of say, 15-20 wives, people would end up inbreeding, whether by accident or not.

Women in monogamous marriages would have more children because that's what they do, women in polygamous marriages would probably only have one child, because out of the harem of 4+ women, if each had one child, that's 4 kids already and the need to breed would be lesser - in comparison to monogamous women who only have their own kids.

I know I've gone on a ramble but that's a really interesting theory of human behaviour.
Humans are the only animal that don't have a set mating pattern, which makes it all the more interesting.

Nowadays. In the past, it was pretty much pure O2, but they stopped doing that when they had a big fire that would have been much more manageable with regular air.

It poisons you.

Nowadays. In the past, it was pretty much pure O2, but they stopped doing that when they had a big fire that would have been much more manageable with regular air.