All animals or plants that are the same kind belong to the same species. Wolves ("Canis lupus") are one species. Humans ("Homo sapiens") are another species. Broadly, the idea is that, for example, cats breed with cats and produce more cats. This is the basis for deciding to have a species called "Felis catus". However, to give a simple definition of 'species' is difficult, and many people have tried.