The Canary Island aboriginal people, the Guanches, are a perplexing mystery to enthusiasts as myself and many anthropologists. There are seven “main” islands and several smaller ones that together make up the Canary Islands, and the one closest to the African mainland is about 350 miles off the African coast, and a brief look at the continental shelf on the west coast of Africa shows that this distance wouldn’t have been that much smaller when the sea levels were much lower 10,000+ years ago, let alone 5,000 or so years ago when the sea level was pretty much the same as it is now.
How could a culture that managed to get to the Islands beyond the horizon of the African coast (from Africa, it is assumed), and managed to settle all of the seven main islands lose knowledge of navigation by sea to the point that they couldn’t even build boats, to the point that not only had they lost connection with the mainland, but the islands had become isolated from each other as well? The former is somewhat conceivable, since the mainland was beyond the horizon, but from any of the seven islands, at least one of them is visible in the horizon in plain sight. Furthermore, most of the islands had abundant forests, which the islanders used to make fire, and it is certain that the boats that they had come on would have been made of wood, so how could they not connect the dots and at least try to build boats? And how could this knowledge be lost or be allowed to not be passed down with utmost care?
One last question: Were the Polynesian seafarers in Easter Island able to leave their island by boat by the time they were visited by Europeans? I recall reading in Collapse by Jared Diamond that they had cut down all of their trees and were therefore unable to build boats (wood logs rot quickly?). I am not sure of whether the problem was that 1) they knew how to navigate the waters, but they couldn’t build the boats needed to do so since they had cut down all of their trees 2) even if they didn’t cut down the trees, they had lost the knowledge of boat building by that time so they wouldn’t be able to make boats anyway.