Seems fairly obvious...

The evolutionary bias towards male offspring could be seen as a balancing act. After all, throughout history, it's always been the men who did the most dangerous jobs. Hunting, fighting rival tribes, coal mining, heavy labour, etc. Men, therefore, are far more likely to die. OK, women, being the child bearers, are at risk of dying, too, but men tended to put themselves at risk on a daily basis, while the most dangerous part of a pregnancy is the actual labour, which is, at the most, once every nine months. It's only in the past 100 years or so that the balance has shifted, men taking up more sedentary roles and women allowed to do the dangerous jobs, too.