In that case, the least intelligent person in the village would almost certainly be significantly smarter than a gorilla, but I think that any chart which puts a very smart humans and a very stupid human almost right next to each other, and a chimp way off to the left, seriously overestimates the distance between humans and other primates relative to the difference between smart and dumb humans.

There was an interesting article which I believe was linked to on Less Wrong at some point, although I can no longer find it, where a professor talked about his time teaching remedial classes for extremely underperforming high schoolers. He found that his entire upbringing and education had effectively isolated him from really stupid people, and left him without a proper sense of just how dumb people can get without being classified as non functional. The students he was trying to teach were not merely unable to perform basic middle school level math, they were unable to grasp the idea that the school was trying to test their math abilities. To them, it was as if someone on high had just arbitrarily decided to ask what the value of A was, and despite his best efforts he couldn't get them to comprehend why it would make a difference whether they were actually able to figure out the answers to the questions or just managed to pick the correct multiple choice options by luck. They essentially lived in a world where, beyond the basic tribal politics and animal-chasing physics for which our brains are optimized, practically everything was opaque and inexplicable.

There may be a very significant intelligence gap between a mildly retarded person and a dog, which can't even pass a mirror test, but the gap between them and a chimp is not that great. It took tens of thousands of years past the development of intellectually modern humans for us to accumulate sufficient developments of culture to start doing more than mildly better than chimps.