since i work in research I know a lot of people with PhDs or people who are working on their PhDs. i think a lot of them are smart, although there are a couple of stupid mfs sprinkled in there.

but intelligence really isn't the most important factor that contributes to someone seeking out and getting a PhD.

someone's access to education is one. getting a PhD is a HUGE sacrifice financially (you are BROKE for 5-7 years+) and not everyone is able to take that financial risk.

second is that simply not everybody knows what a PhD is or how attainable it could otherwise be for them. the people most likely to get PhDs are people who are NOT first generation college students.

there are lots of socioeconomic and cultural factors beyond intelligence that play into it. it's not simply a question of whether the individual is smart enough to do it