CoachTo classify living things is to sort them by shared body features into groups, and to sort those groups into bigger groups — groups nested inside groups, like boxes in boxes. The whole arrangement is a classification.
Examples
Example 21.2 (The cat’s addresses)
One cat, several nested addresses: the cat is a mammal (fur, milk for the young); every mammal is a vertebrate (a skeleton with a backbone inside); every vertebrate is an animal. Cat inside mammals, mammals inside vertebrates, vertebrates inside animals: each box sits inside a bigger one.
Example 21.9 (A new species arrives)
Naturalists still discover animals never seen before. When a new bat-like animal is found with fur and milk, it goes straight into the mammals — and at once biologists expect a backbone, a four-chambered heart and warm blood, before any of it is checked. The classification pays out predictions.