Hello there!
1) From a historical/nomadic stand point, three possible reasons to move would be:
* To change locations as the weather changes.
* To follow the herds of animals.
* As a tradesman or craftsman, travelling was needed to exchange goods or to practice their craft in certain places. Therefore, they were not capable of sustaining a community in a sedentary lifestyle.
2) Humans have been on earth for an estimated 200,000 years
Hope this could be of use to you.
