There was very little diffusion few thousand years ago, [his putative dating]. Indo-European counterclockwise swing did happen in that time frame, but did not impact on the East Asians, and surely did not impact on the population of the Americas. That's why I question his timing - from Occam's principle it would be so much simpler to date that mutation [or the whole cascade of them] to as yet undifferentiated out-of-Africa group [100-110 to ca.40 Kyrs before the present]. More, such time conveniently pre-dates the settlement of the Americas.
A week or two ago, the GGG ping group posted something that suggested that the earliest inhabitants of North America were closely related to Australians, while the Asiatics whom Native Americans are related to were more recent.
Since the smartest people in the world are Asians and Jews, not likely a "smartness" mutation originated in Europe or among Indo-Europeans.