Classifying life

There are millions of different living things on Earth, from the tiny beetle to the huge whale. To keep track of them all, biologists sort every living thing into groups. They watch for shared features: how a body is built, how a living thing reproduces, and how it gets its food.

Kingdoms and classes

At the very top are large groups, the kingdoms. Animals and plants, for example, are two different kingdoms, and the fungi form a third kingdom of their own: a mushroom is not a plant. Within the animals there are smaller groups, the classes, for example mammals, birds, amphibians, fish, and insects. Each class has typical features by which you recognize it.

Vertebrates and invertebrates

One important feature is the backbone. Animals with a backbone are called vertebrates, and these include mammals, birds, reptiles such as snakes and lizards, amphibians, and fish. Animals without a backbone are called invertebrates, for example insects, spiders, and worms. This single feature splits the whole animal world into two large groups.

The identification key

Many shared features are a clue that living things are closely related. To place an unknown animal, you use an identification key. It is a chain of yes or no questions: Does it have a backbone? Does it have feathers? Step by step you arrive at the right group.