Classification is an ordered set of related categories. This is also called Taxonomy. There are seven ways of classifying this. As you move down the levels of classification the living things become more and more similar to each other. Before people started to recognize the similarities and differences of different organisms, people still sought a means to organize biological diversity. In 1758 Carl Linn proposed a theory of a system that has dominated classification for centuries. Linnaeus have each species two names, denoting genus and species (like Homo sapiens). He then started to put together larger groups like genera into families, families into orders, orders into classes, classes into phyla, and phyla into kingdoms. The two kingdoms he identifies first were Animalia (animals) and Plantae (Plants). As science improved kingdoms and other classifications expanded into more specific names. The reason we classify things is to get things into groups and categories to help us stay organized and keep track of certain things so we can compare them.