And this is still preventing many species from crossing today when sea levels are higher and the continents are fragmented into neighboring groups of islands.

而这在今天仍然阻止着许多物种的跨越，因为当海平面升高时，大陆会被分割成相邻的岛屿群。

And if they see a " stranger" —“stranger” in quotes: that's an individual from a neighboring social group—usually, if it's one by him or herself, they chase.

如果他们看到一个“陌生人”——加引号的“陌生人”：那是来自邻近社群的猩猩——通常，如果是他或她自己单独一只，他们就会去追。