at any one time in history, there are millions of different kinds of plants and animals in the world. In 1753, a scientist in Sweden named Carolus Linnaeus thought of an orderly system for classifying plants and animals. He grouped all organisms according to a two-part name (binomial). The first part of the name is the "generic" grouping or genus. The second part is the "specific" grouping or species. Scientists today still use this basic idea of his system, but modern classification systems are much more complicated having many levels of hierarchical organization. For example, taxonomic systems group organisms according to structure and physiological connections between organisms.