Sorting Living Things

Trees, insects, mushrooms, and birds are just four of the millions of different kinds of living things in the world. How do we keep track of them all? Scientists use a system called classification. Classification is a way of creating order by putting things in groups. You classify your clothes when you put them away. Socks go in one drawer and T-shirts go in another. In the same way, scientists sort living things based on the many ways in which they are alike. Most scientists sort living things into five or six kingdoms. A kingdom is sorted into smaller groups. The groups narrow to a single type, or species, of living thing. One group in the animal kingdom is animals with backbones, or vertebrates.

Animals with backbones can be sorted into fish, amphibians, birds, mammals, and reptiles, such as this American alligator. View Larger Image

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