Essentially, we humans live well enough and long enough, and are smart enough, to generate all sorts of stressful events purely in our heads.

We're getting along so well; I trust you so much for this one second that I'm going to let you yank on me.

Hormones influencing the sensitivity of the person to environmental stimuli.

If a rat is a good model for your emotional life, you're in big trouble.

If you live in a baboon troop in the Serengeti, you only have to work three hours a day for your calories, and predators don't mess with you much. What that means is you've got nine hours of free time every day to devote to generating psychological stress toward other animals in your troop. So the baboon is a wonderful model for living well enough and long enough to pay the price for all the social-stressor nonsense that they create for each other. They're just like us: They're not getting done in by predators and famines, they're getting done in by each other.

It's great to have a buff frontal cortex to do that harder thing - for example, help a person in need rather buy some useless, shiny gee-gaw.

We live well enough to have the luxury to get ourselves sick with purely social, psychological stress.