My theory about shyness

I think that shy cautious people may be more like this is survive in many environments but older people are more likely nto have children because they will find it easier to look for mates But you only need one mate to have a child and in our society sex is mainly a form of reparation since contraception is easily available. So the bold may not have any more children than the shy.

and the most sexual partners you have the more likely you are to have sexually transmitted diseases. That might be the reason why extroverts might die young.