Scientists Say: Species

This word describes organisms that share similarities in physical traits and genetics

The group of insects known as beetles includes over 360,000 different species.

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Species (noun, “SPEE-shees”)

This is a word that describes organisms that share genetic and physical traits and are more closely related to each other than to any other group. Scientists sometimes define species as a group of organisms with members that meet two requirements. First, two individuals from the group must be able to reproduce and make healthy young. Second, those young must also be able to have offspring of their own. But this definition works better for some living things than others. For many living things that reproduce sexually, meaning that two parents both contribute genetic material to their offspring, this definition is usually fine. Not all living things have two parents, though. For example, most bacteria reproduce by making a copy of their genetic material. Then they split into two new individuals.

Even among animals, the traditional definition of species doesn’t always fit. Most animals of different species don’t mate. For instance, a bat can’t mate with a cat. But closely related species sometimes do. This makes what’s called a hybrid. Often, these animals are sterile. That means they can’t have offspring. Mules are one such hybrid. Mules have one donkey parent and one horse parent. Other hybrids, like the offspring of grizzly and polar bears, can reproduce. The result are pizzly or grolar bears. Whether hybrids like these make up a new species is part of the quandary around species.

Pinning down an exact definition for the term “species” may be difficult. Yet the concept is valuable to many people. It helps scientists keep track of biological diversity on Earth. It also helps people who make laws to protect wildlife. Being able to catalog the diversity of microbes, plants and animals helps scientists and others figure out how these living things relate within an ecosystem.

In a sentence

Because of human activities, a million species could go extinct.

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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