Before decent agriculture was established, man lived off of what he hunted and gathered. Being tied to one location was only a benefit if that location had what was needed. As timber and other natural resources get depleted in an area, going over the next mountain or body of water often revealed better conditions.
Combine that with the natural drive some humans have to explore and discover, and it makes perfect sense to me that people got around more than many people would think. Todays human looks at a long trip in the wilderness as a hardship because life is easier at home with food, warmth, clean water, etc all close at hand. Back then, landing on a beach in a new land with abundant game, uncut timber, untouched water supplies and only a relative handful of people, and suddenly life on the road is better than life at home. Throw in some motivation added by a few years of drought, extreme cold or unfriendly neighbors, and some traveling looks pretty good.
If a few Inuit kayaked from Labrador to Scotland in recorded history, I imagine that in the thousands of years prior to that the connection was made more than once both ways. Once on a new land, its pretty easy to follow coast lines and cover a lot of ground.
