The labour involved in raising kids has a higher opportunity cost for more competent people. Also due to regression to the mean, very intelligent people are unlikely to have children smarter than them so this may reduce rewards.
Intelligent, rational people not having kids is basically a tragedy of the commons. Everyone is better of (including the unintelligent and irrational) if this group has more children, but for each individual it is a pretty burdensome undertaking (even when taking into account selfish reasons to have kids) And our whole modern status system is unfortunately built in such a way that it exacerbates the problem rather than alleviating it.
The labour involved in raising kids has a higher opportunity cost for more competent people. Also due to regression to the mean, very intelligent people are unlikely to have children smarter than them so this may reduce rewards.
Intelligent, rational people not having kids is basically a tragedy of the commons. Everyone is better of (including the unintelligent and irrational) if this group has more children, but for each individual it is a pretty burdensome undertaking (even when taking into account selfish reasons to have kids) And our whole modern status system is unfortunately built in such a way that it exacerbates the problem rather than alleviating it.