Up to 85% of people have a vestigial muscle called the " palmaris longus."

多达85％的人有一种叫做“掌长”的退。

Looking at our primate relatives, we can see that the palmaris longus is sometimes absent in those that spend more time on the land, but always present in those that spend more time in trees.

察一下我们的灵长类动物祖先，我们可以发现，那些在陆地上生活更久的动物有时没有掌长，但是，那些在树上生活更久的动物总是有掌长。