Because male fetuses are more fragile than female fetuses, they are more likely to be damaged.

Statistically, it is clearly true; compared to men, (women) are biological fortresses.

You get rid of the weak, and on average the cohort lives longer.

One argument is that it was conserved to help us lift buses off of pedestrians who just got hit. My belief is that nature conserved the stress mechanism because of its effect on gestation. Natural selection doesn't care about individuals, it just wants poundage and conservation of genes. It found a way to maximize the pounds and the genes.

These findings demonstrate yet again that we need not go to museums of natural history to find evidence of natural selection.

We can never use humans to directly test out the theories. We can only make inferences based on natural observation.

The culled-cohort theory is based on the assumption that it is not in the mother's interest to have small or weak male offspring during times of stress. Weak males are less likely to survive to age of reproduction. Even if they do survive, they must then compete with strong males for females.

It's not in her evolutionary interest to have a weak son in times of stress. He may not survive or may not be competitive for females.

The argument is that in most species, males will compete with each other for females, and females prefer robust males.