That makes no sense to me because for every child a daughter has, someone's son had a child. It has to balance out unless someone invents monkey mitosis.
It doesn't. In a species with 50/50 split between male and female, the number of males is almost irrelevant to population growth. Take rabbits. If you kill at birth 90% of the males, the population growth won't slow as the limit is the number of babies per-female. The 10% of males that survive simply father more kids via more females. Males can do that. Females cannot. Going one step further, killing all those males increases the resources available to the females. Ironically, culling those males can cause a population to grow faster than if they lived.
> In a species with 50/50 split between male and female, the number of males is almost irrelevant to population growth.
The split between male and female isn't relevant to this. Unless the males are needed to raise the children, the number of males is irrelevant to population growth.
But the average benefit of having a son remains equal to the average benefit of having a daughter; that's why the ratio stays at 50/50.
In nature, males can impregnate many females and do not have to necessarily be around to rear their many offspring. So it is advantageous to have many females that can procreate with less males to increase the population size at a higher rate than more males and less females to mate with.
Indications from genetic research are that humans may have about twice as many female ancestors as male according to some theory about discrepancy in the "time to most recent common ancestor" for mitochondrial DNA (extrapolating for female ancestors) and the nonrecombining portion of the Y chromosome (extrapolating for male ancestors).
I think the presence discrepancy is reasonably well accepted.
