Because people who are born lucky enough to have an easy life are likely to have more kids.
Using cortisol to magnify that improves selection bias.
The rest is math.
Evolution is a bitch.
what does “recent” mean? Poor folks been having shit tons of kids for a long ass time. THey needed to have a) extra workers, and b) a chance at keeping the family name/heritage/culture/whatever going. especialyl being poor, you know at least 3 or your 10 arent going to make it, so you gotta play the odds!
A successful organism would not have evolved to highly express cortisol to weed itself out in the case that it has a stressful life. It makes no sense for an organism to evolve a trait that makes it at best equally likely and at worst less likely to reproduce.
The reason we release excess cortisol in modern life is because our bodies did not evolve for constantly present stressors, they evolved to be stressed in a situation, run away from the tiger, and then you’re good.
