Peopling of the Americas

Genetics supports roughly three or four entries into the Americas, not dozens: the founding dispersal ~15–16 kya that split into northern and southern branches and produced nearly everyone from Canada to Tierra del Fuego; a later Siberian-related stream carrying Na-Dene ancestry; Paleo-Eskimo ~5 kya; and the Thule/Inuit-Yupik expansion ~1,000 years ago. There is also an unexplained faint Australasian signal ("Population Y") in some Amazonian groups.

Language families tell a different story, around 150–180 that can't be shown to descend from each other, but that's 15,000 years of in-place diversification plus the ~8–10 kya ceiling on the comparative method, not 180 arrivals. "Wave" is a simplification throughout: these were ongoing movements and back-migrations, and the Na-Dene signal is admixture layered onto first-wave ancestry rather than a clean separate population.