What is 'general intelligence'? (Anything like Colonel Panic?)
Yes, if you can't read, can't figure out a bus schedule you are in a world of hurt in this society. It does not follow that being able to understand calculus gives you peace, happiness and longevity. There is going to be some broad mean that societal requirements dictate that you need. Other than than, you are at the mercy of lots of other vagaries of life.