I would assume that an Atheist could be as stupid as a Theist. I would imagine that even an Atheist could be dumb enough to doubt Evolution. It's a little harder for the Atheist but that simply makes it a bigger challenge. The Theist has a slight advantage cause they could use Goddit but the Atheist could also believe that things just happened without evolution or Goddit.
The bottom line is anybody who is not in someway mentally handicapped or wilfully ignorant must accept evolution based on the overwhelming preponderance of evidence.