Only when these hominids had to travel between arboreal habitats would they find themselves walking bipedally, 'forced' to do so by their own anatomies.

“只有当这些人科动物在两棵树上的栖息地之间来回穿梭时，他们才不得不用两足来行走。由于他们骨骼的结构特点，他们是‘被迫’这么做的。”

The more these animals started to walk on all fours and then with us to walk bipedally, the tails were not useful any longer, and so it was pushed to the side, it became a vestige.

这些动物越开始用四肢行走，然后和我们一起两足行走，尾巴不再有用了，所以它被推到一边，它成了一个残留部分。