As primary nurturers, it seems fitting that women should have more of the hormone in their systems than men. Looked at another way, as the ones responsible for fighting wars, rescuing babies from collapsed buildings, and rousting cat burglars from the basement, it seems fitting that men should also have less of it. We ve inherited this ability to tune out pain from our primate cousins. Dependent on others for survival, they need to be as socially appealing as possible. Levels of the hormone diminish as the animals approach puberty, when it stabilizes.
Females end up with more, males with less.
The amount of the chemical circulating in the primate brain seems calibrated to each sex s adult-life agenda. Males, on the other hand, break from their troop as young adults and can spend a couple of years in kick-ass male gangs before being accepted into another. For them, their separation is like a walk in the park. By depriving them of serotonin and thus blunting their stress response, nature protects them against the pain of striking out on their own. The males, and their species, are better served by their feeling too little than by feeling too much.