first, what makes you think that religious people are necessarily stupid?
there are huge numbers of intelligent religious people. that a person is religious doesn't mean they aren't also smart. indeed, just the statistics alone tell us that most smart people are religious. we can see this by considering that most people are believers in god and that means that most people that are smart believe in god. sure, a fewer number of people that are smart believe in god than don't (the more educated you are the less likely you are to believe in nonsense, and surveys of the Royal Society and the American Academy of Science tell us that the most eminent scientists are highly unlikely to believe in a personal god), but that doesn't mean that atheists have a stranglehold on intelligence.
indeed, there seem to be a significant number of atheists that are far less intelligent than the intelligent believers.
as Michael Shermer has pointed out when talking about belief and intelligence (paraphrasing), intelligent believers are just more capable of coming up with rationalizations for beliefs they arrived at for non-smart reasons. it doesn't mean that there are no smart religious people.
second, everyone is really impressionable. evolution has instilled in us a natural trust of our parents and the adults around us because it's more likely than not that they'll have the information to ensure our survival as children. also, we're just not good at abstract reasoning. it's a learned skill, not a trait we're born with. we didn't need to be good at abstract reasoning in order to survive in the environments in which evolution provided us with the cognitive mechanisms we do have.
third, yes, there has been a great deal of research into evolved cognitive mechanisms that produce in us religious thought. i could suggest several books but the general idea is that we evolved pattern recognition and agent detection mechanisms and that these misfire leading us to spot patters and agency where none actually exists.
thanks for your input. I didn't mean to give the impression that I think religious people are stupid. I was just having a conversation with a friend of mine today and he was talking about genesis and how many holes in it. And he thinks that only people that lack critical thinking skills could possibly believe in the bible. but I watched a video on this subject on Youtube, Which made me want to know if other people thought this way as well. My fathers pretty intelligent and he's a devout christian.
Consider, if you will a deranged, delusional, hallucinating madman who, when you fail to accept his rants, murders you. Your genes, for reason, logic, and sanity are being removed from the gene pool while he continues to reproduce. Now, do this over thousand's of years, and evolution suggests that reason, logic, and sanity will be reduced in the population, and deranged, delusional, hallucinating madmen will increase.