For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another.
例如，在过去的冰河时代，冰川向下穿过北美和欧洲，逐渐切断了部分人口之间的联系。
3
The number of North Americans who went to the cinema in 2010 was around 5% down on the 2009 total, figures show.