In this topic you will learn about how to classify living things to help you understand their similarities and differences better.

To make order, or sense, out of the variety of living things, scientists organize, or classify, them into categories. The largest group used to classify living things is called a kingdom. Two of the kingdoms are the plant kingdom and the animal kingdom. The kingdoms are divided into smaller groups based on the similarities of organisms.

For example, the animal kingdom is divided into several phyla. A phylum is a main group within a kingdom, whose members share a main characteristic. A phylum is divided into smaller groups called classes. The class Mammalia includes all animals that have fur or hair and produce milk for their young. Members of a class that have the most in common are put into smaller groups called orders. The most similar members of an order are grouped into a family. The most similar family members are grouped into a genus. The most similar members of a genus belong to a species. All members of a species can mate and reproduce more of their own kind. A species has the most similar members in a kingdom.

Each living thing is given a scientific name. A scientific name is a two-word term for a living thing, based on its classification. The two words consist of genus and species. Latin is used in scientific names. The genus name always starts with a capital letter. The scientific name for timber wolf is Canis lupus. A coyote is Canis latrans and a dog is Canis familiaris.

Organisms in a phylum are grouped according to body structure. Both humans and dolphins have backbones, which makes them members of the same phylum, Chordata. Body structures often show that living things may have had a common ancestor.

By comparing structures closely, scientists began to realize that more than two kingdoms were needed to classify organisms. Scientists saw that one-celled organisms were different from many-celled organisms. They knew that one-celled organisms did not belong in the plant and animal kingdoms.

DNA is found in the chromosomes of all living things. Each living thing has a distinct pattern of the pieces that make up DNA. DNA helps in identifying an organism, almost like fingerprints. Closely related organisms have more similar DNA.

Scientists continue to classify the organisms they discover. Classification helps in understanding the similarities and the differences between organisms.