Wow, that completely changes my perception of history.

There are two competing theories on the initial population of the Americas. The first was a land bridge theory which suggests hunter-gatherers tracked mammoths across the once-frozen Bering Strait bridge of modern Russia/Alaska, but a newer and more popular theory is that Polynesian peoples arrived by boat navigation.

Apparently, sweet potatoes arrived in Polynesia around 1,200 and 1,300 AD, which gives a lot of credit to the idea that the first human inhabitants of the Americas arrived by boat from Polynesia.