1、适者生存。survival of the fittest;

2、[例句]随着世界气候的变迁，恐龙绝迹了，但许多较小的动物却继续活了下来。这就是适者生存。

3、With the changes in the world\\\'s climate, dinosaurs died, but many smaller animals lived on. It was the survival of the fittest.