If men had genetically superior immune systems, this would be our rationale for paying more attention to female health, women are fragile, women need protection. However, women’s double-X chromosomes give them a kind of genetic backup system 17 That is, if a woman has a defective gene along one thread of her X chromosome, the odds are very high that the matching gene on the other X will be perfect.18 Men don’t have that backup system.

So while women have that initial advantage, it is not an all-encompassing advantage. In birds, butterflies, and moths, it is the males who have this genetic backup system and the males still die sooner.19 And in humans, almost all premature deaths after the first year are related to stress-induced diseases and pressures related to men’s role – from suicides to heart attacks, from cancer to murder.

More powerfully, the vulnerability of men because of their social role cannot be separated from their vulnerability because of their biology. For example, when men reflexively rescue women, they are not only more likely to get physically stabbed, shot, or punched but these rescuing behaviors generate "emergency hormones.’’ For examples, testosterone is generated, but testosterone weakens his immune system;20 adrenaline (or epinephrine) is generated, but adrenaline also causes his blood to be more likely to clot, making him more vulnerable to heart failure.

Just as countries build missiles "just in case" and then find the cost of those missiles has taxed their ability to strengthen themselves in other ways, men similarly pay a biological price for their external role as women’s constantly available, unpaid bodyguards.