What Is a Species?

A species is a group of living things that share many important features and, in most cases, can reproduce with one another. Dogs are one species. Domestic cats are another. Humans are another. But nature does not always draw lines as neatly as a textbook might.

Some species vary a great deal. Think of dogs: a dachshund and a Great Dane look very different, but they belong to the same species because humans have bred dogs from the same ancestral population. In the wild, variation can also be wide. A plant species may have taller forms in wet soil and shorter forms