J1c is relatively diverse, geographically speaking. It is interesting that we seem so focused on land routes, as many--if not most--of these migrations occurred by boat. Why bother cutting through prehistoric forests and scaling formidable mountain ranges when you could travel the path of least resistance? Waterways were the highways of the ancients. But whether J's diffusion is due to the use of watercraft or slow movements across land over time--that is an interesting question.