Intelligence is probably at least partially inheritable. If intelligent people have fewer children you expect intelligence to go down eventually.
Just because smart people tend to have fewer children (because, for instance, they delay it due to schooling and career demands) doesn't mean genes for intelligence are necessarily being selected against.
Just because smart people tend to have fewer children (because, for instance, they delay it due to schooling and career demands) doesn't mean genes for intelligence are necessarily being selected against.