First of all, not being intelligent is not a 'bad' characteristic. Someone who isn't deemed as clever as someone else isn't any worse a person.
Secondly, I guess not being 'intelligent' does make you less likely to be a PhD student. Because postgraduate studies assume a certain level of intelligence, judged against previous study. Certainly, perseverance and a passion for the subject play a big role in a PhD, but surely a certain level of intelligence is required too.
Sorry Maria, but I don't really understand your post?