 From amoebas to artworks and fungus to fruit trees, what does it mean to classify organisms? Why do we do it? And how is it done? Classifying anything simply means to put it into a group. In terms of biological classification, organisms are classified or grouped with other organisms that they are most closely related to. These small groups are then classified together into larger groups and so on, until we reach the top level of classification, which places organisms in one of three biological domains. Archaea, Bacteria and Eukaryea. When each organism is classified in this way, it allows scientists to see the relationships between different species and make sense of a hugely diverse array of life. Modern systems of biological classifications, or taxonomy, are based on the work of a pioneering 18th century scientist called Carl Linnaeus. By studying hundreds of organisms, Linnaeus devised a method of grouping them according to their shared physical features. Those with similar physical features could be classified together. The most similar organisms, i.e. those that could breed together and produce fertile offspring, were designated as belonging to the same species and given a Latin species name accordingly. For example, all domestic dog breeds belong to the same species called Canis lupus familiaris. Other members of the dog family that are closely related but not the same species will share the higher group name, the genus name, but have a different species name. For example, the gray wolf, which is the closest relative to the domestic dog, is classified as Canis lupus lupus. By using this system, we can classify organisms according to their shared evolutionary history. Linnaeus also created higher and more inclusive taxonomic categories that encompass an increasingly broader range of organisms. The structure of Linnaeus's taxonomic groups can be seen here. You can make up a little rhyme or acronym to remember this, such as keep ponds clean or frogs get sick. By using this system of common groupings, we can develop diagrams that show the interrelatedness of organisms based on their morphological diversity. For example, this diagram of a taxonomic tree shows that humans are more closely related to chimpanzees than they are to gorillas. A common ancestor is represented by each split in the branches of the taxonomic tree. How long ago did humans and gorillas diverge from an evolutionary perspective? Recent advances in science, including the ability to categorize DNA sequences, have enabled scientists to accurately determine how closely species are related to each other. This has led to the revision of the original grouping suggested by Linnaeus. New organisms are constantly being discovered, and relationships between organisms are changing all the time, so the importance of a taxonomic study to modern science cannot be underestimated.