Having surviving children was the preserve of the cleverest.
The entrenched aristocracies around the world, many of which survive to this day, along with the Neo-feudalism now cutting off social mobility in the U.S. pretty much makes that claim a lie, at least for a few generations. We aren't ruled by 'the best and brightest'; even G.W. Bush made it through the 'elite Ivy League' schools all the way through grad school. Also, being 'intelligent' doesn't necessarily mean 'good', as Rhodes Scholar and serial rapist Bill Clinton's degeneracy clearly shows.
Guess it should be a thread topic somewhere.