Good question. There are believed to have been several migrations, and I think the Kon-Tiki proved that SA was reachable by reed boat from ... Africa? ... I forget.
Oh, yeah, I vaguely remember that. I didn't know if they had really accepted it, it seems to me like a long journey to bring enough people to start a civilization by boat, but maybe they've decided it was possible or likely. It's been a LONG time since I've read anything about that.
susie
My recolection is that Thor Hyerdahl sailed his blsa-wood raft from Peru to Polyonesia via the Humbolt Current.