This is an incredibly fascinating topic, Paul. By using genetic markers, some clever people actually traced the chronology of the path of these prehistoric migrations. Take a look at this:

https://genographic.nationalgeographic.com/human-journey/

There are other links in the above, to focus on certain routes.

This link describes the techniques used:

http://science.howstuffworks.com/life/evolution/human-migration3.htm

Amazing subject.

I'm fully convinced that Neolithic and Mesolithic peoples followed specified routes. The commonality between routes is too statistically significant to be coincidental.