Actually all professions are much more stratified by intelligence than in the past (this is side effect of meritocracy). There is lots of research on this - this is just the first paper I found on google [1].

In regards the rulers have a look at their educational background. In the roles that really matter they are all very clever.

1. https://www.staff.ncl.ac.uk/daniel.nettle/britishjournalpsyc...