@Lex Fridman As for how many times Civilization can respawn .... I assume you have heard of the Olmec. They carved giant stone  heads with distinctly different features of any race to live in Central America. Gram Hancock’s book says there is new DNA linking Aborigines to some of the lost tribes in central and South America. It seems they came over the ice age before the Japaneese Nomads that came across the ice bridge to settle the Americas. Like Egypt the best work of the Aztec seems to be at the beginning like they were slowly loosing the knowledge of more advanced Tribes before them