It is laughable to think that the first supported travel over water was done in “boats“ or by “sailing“. Children instinctively climb onto floating objects. It seems very likely to be that some unwary homo-something crossed an unswimmable span of water quite by accident and survived. Perhaps some other individual observed their fate and followed, perhaps from the same species or perhaps not. Perhaps alone, or perhaps with others.
The evidence is merely that there are early tools on islands.
About 40 million years ago, some monkeys in Africa evidently floated a few thousand kilometers across the ocean to South America, probably on driftwood. Neanderthals were a lot bigger than those monkeys, but a similar scenario might have happened here.
