Thinking positively: The genetics of high intelligence

I would be very surprised if high intelligence was anything other than the extreme edge of a normal distribution of the human population. For it to be anything other than this it would require people of high intelligence to be a sub-population that did not breed with the rest of humanity.

You could make this argument for any trait. However, some traits are the result of a single gene - e.g., sickle cell anemia and the accompanying malaria resistance. Yet some of these traits occur in large populations that are not strongly inbred.

Only single gene traits. Intelligence (however defined) is multi-genetic - there are thousands of genes that contribute to intelligence. Given this the only way that individuals with high intelligence could be anything other than edge of a normal distribution is if they were part of a human sub-population.

Edit. I should add that the humans are not completely one population because of genetic isolation and differential selection (especially over the last 10,000 years), but we are almost a single population. Like everything in genetics it gets fuzzy at the edges.