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。
For example, during past ice ages, glaciers advanced down through North America and Europe and gradually cut off parts of populations from one another.
到二十世纪初，科学家们认为，在更新世期间，有四次不同的冰川作用对北美和欧洲产生了影响。
By the early part of the twentieth century, scientists believed that four distinct glaciations had affected North America and Europe during the Pleistocene epoch.
在北美和欧洲，像荷兰榆树病这样的真菌疾病已经杀死了数百万棵曾给森林和城市增光添彩的高大树木。
In both North America and Europe, fungus-causing diseases such as Dutch elm disease have killed off millions of stately trees that once gave beauty to forests and cities.
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