That made some populations mobile because they had to move from place to place to find food, but of course, it made starvation a very real possibility.

那样使得部分人口开始流动,人们不得不不断地迁徙,寻找食物,当然 自然灾害也造成了饥荒

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

They were always mobile, always going somewhere, always changing.

他们总是流动的,总有新的目的地,总是不断变化着的

耶鲁公开课 - 美国内战与重建课程节选