Yes, a good point. But weren't these American Indians mostly hunter-gatherers? I don't know if you can say that they engaged in agriculture. Some other tribes did, but those didn't rely on nuts or acorns.
Eh, to my mind the boundary between agriculture and gathering is fuzzy when your plants live a long time and grow pretty thickly and you encourage the growth of those you like.
Like, there's 11.5k year old seedless fig trees found in the middle east, a thousand years before there's any evidence of grain field agriculture. Those simply don't grow unless planted by humans.
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