How they manage to know one thing around here, but not another... probably the concept of an equilibrium appeared in wizardry, even though, apparently, wizards don't already know calculus?? At least at their level?
"Right. Any time you've got pressures on something, moving it, it'll keep moving for so long as the pressures are balanced. Half male and half female represents a balance of something, which is why it's like that - but what is it that's balancing? We have thoughts like 'well, if it was ten times as many women as men, or ten times as many men as women, then a women who had all male children or all female children would have more grandchildren'. But that doesn't explain how it's a pressure - how it would be able to move the system's mix of men and women, if that mix wasn't already fifty-fifty. How can we get from 'in a country with ten times as many women as men, one woman with all male children would have ten times as many grandchildren', to, 'there is a pressure that will move the average mix of men and women if it isn't already one-to-one'?"