South Korean babies born on December 31 become 2-year-olds the next day.

[PoindexterOglethorpe]

13. Native Americans did domestic horses

once modern horses got to this continent.

The ancestors of horses started here, but left long before they became modern horses and vastly long before the original humans we call Native Americans arrived.

But yeah, just have some modern horses (or sufficiently close relatives of them) come across from Siberia when the land bridge was in place. That's plausible enough. The people already here or soon to arrive would have domesticated them in pretty short order. I'd love to read that alternate history.

It's hard to know if a technological civilization would have happened just because of the horse, but I think the case can be made for a lot more trading pretty much from edge to edge, north to south, east to west. And perhaps a genuine system of writing would have sprung up to keep records, which is pretty much how writing got its start in the Middle East. I don't know enough about the history of the Far East to know for sure what triggered the writing systems there, but I wouldn't be at all surprised if record keeping was the impetus there also. Hmmm. Real food for thought here.