Birds eat seeds.
Birds migrate thousands of miles.
Birds poop.
Bird poop is good fertilizer.
Lots of real small lakes or real large ponds were populated with fish from eggs pooped out by seagulls......
So, we can blame sweet potatoes on the poor bathroom habits of birds?
Yep - I thought of birds right off. I can’t imagine their being an west-east migration route, but perhaps a bird getting caught up in a storm would do it. Although I’m not sure that is the direction of normal weather patterns. But - give things 5,000 years to happen, I’m guessing the odds are for a bird making it to Asia from South America.