The idea makes a certain amount of sense, but it seems to me that the sample size (of continents) is rather low.

Africa is 4,500 miles wide from Senegal to Somalia.

Also, it's not clear that changing latitude within the tropics is as difficult as in the temperate zone. To go from 30 degrees north to 45 north to 60 is a challenge, whether for corn or for human beings.

To go from, say, 15 degrees north to the equator to 15 degrees south doesn't seem as big a deal, although I may be overlooking something.

I'm unconvinced by the underlying logic of the whole premise. (Big brain / better adoption of ideas = greater selective advantage on larger, wider continents.)

How many new ideas were likely to filter into a far-flung village per generation? One idea? None? When an idea DID filter in, it would likely be adopted quickly by the entire community, and would thus quickly negate any selective advantage bestowed on the early adopter.