Fertility goes down as wealth increases because developed industrial societies don't use child labor and infant mortality has gone way down. It's not because intelligence is a disadvantage.

You know, generally as wealth increases birth rate decreases. Just look at the population crises coming up around the developed world.

This is the exact opposite of why people are having fewer kids in areas with population crises.

People generally have fewer kids in developed nations than in developing nations because all of their children are likely to survive.

Population crises arise due to social and economic factors.