A wider choice of mates reduces people's reproductive output.

The real reason: people in rich countries have been tamed to be orderly cells inside larger and longer-lived organisms -- the nation, the culture, a religion or class or movement, a corporation, whatever.<p>Within a larger organism, there's no surprise individual cells don't wildly reproduce in the organism's warm, safe, nutrient-rich environment. That's against the conditions of formation/inclusion. When it happens, it's often a cancer that threatens the whole.

what do rich cultures have in common? they are civilized enough to get rich. they have good enough values that let them cooperate peacefully with others, etc<p>the sort of good values that make societies richer include caring about your children individually and spending much more money per child, instead of just trying to have a lot of kids and use them for cheap labor.<p>also, our culture considers children a pain in the ass. then people wonder why we aren't having as many as we used to? because more people are doing what they want instead of blindly following tradition.