A ASPM gene, which is one of handful genes making a difference between chimpanzees and humans and is thought to be responsible for the explosive growth of our brain capacity, have had the last mutation at 5,800 years ago, which coincides with the introduction of the written language and agriculture.
Age of Kennewick Man, who is an ancestor of Native Americans and found at Kennewick City, was analyzed 9,000 years old. That date is before of last mutation of the ASPM.
How interesting! It might mean that he and his ancestor mentally, brain structurally saw a different world during their migration journey, from Asia to America, from one I saw during kayak journeys along North America. And it might mean that I cannot trace a exactly same experiment of their, because we are walking along a evolution high-way and never rest.