The Linnaean classification system of organisms was developed in 1758 by a Swedish botanist named Carl Linnaeus. He was also known as Carl von Linné and Carolus Linnaeus, the latter of which was his Latin name.

All living things on Earth are descended from a single common ancestor. Species branched off at different points in evolutionary history, and then again split off many times more, until there were millions of species – and most are still undiscovered by humans to this day.

Humans have been attempting to sort and name organisms for thousands of years. This practice is called taxonomy, or Linnaean enterprise. Modern taxonomy is still based on the Linnaean system. You might also see that name spelled as "Linnean" when used as an adjective, such as with the Linnean Society of London.

One of the better known examples from human history of an attempt at the taxonomy of organisms comes from Aristotle. His ideas built on those of his teacher Plato and others.

Aristotle’s system of classification bore the name Scalae Naturae, which means the "Ladder of Life" when translated from the Latin. It is also called the "Chain of Being." Aristotle was developing his theories in approximately 350 B.C., so he lacked any knowledge of genetics or evolution.

Given the relative vacuum of acquired human knowledge in which he was formulating his ideas, he was unable to formulate a system of classification that holds up under modern scientific scrutiny. It was, however, the most comprehensive theory of biological classification that had been developed until then.

Aristotlean taxonomy divided animals into those with blood, and those without. The blooded animals were further divided into five genera (the plural of genus; this is also a term used by modern classification of species, but in a different manner). These were:

• Viviparous animals (mammalian quadrupeds) that give birth to live offspring.
• Birds.
• Oviparous animals (amphibian and reptilian quadrupeds) that lay eggs inside of which the offspring mature and then hatch.
• Whales (whales are mammals, but this was not known to Aristotle).
• Fish.

The bloodless animals were divided into another five genera:

• Cephalopods (octopi, squid and cuttlefish, for example).
• Crustaceans (crabs, barnacles and lobsters, for example).
• Insects (in addition to insects such as beetles, flies and mosquitoes, Aristotle included scorpions, centipedes and spiders, although these are not considered insects now).
• Shelled animals such as molluscs (snails and scallops, for example) and echinoderms (starfish and sea cucumbers, for example).
• Zoophytes or “plant-animals,” which were animals that looked like plants, such as cnidarians (anemones and corals for example).

While Aristotle’s system was insightful for the time, he did not base it on true genetic or evolutionary relatedness. Instead, it was based on shared observable characteristics and used a straightforward classification scheme of simple to complex, from the bottom of the “ladder” to the top.

Aristotle placed the human species at the top of the ladder, since humans possessed a singular ability to think and reason in the animal kingdom.

Carl Linnaeus is considered the father of modern ecology and the father of taxonomy. Although many philosophers and scientists began the work of biological classification before him, his work in particular provided a foundational system for sorting and conceptualizing living organisms that has lasted since the 1700s.

Modern scientists have proposed and implemented a number of changes to Linnaean classification in order to account for ever-expanding knowledge of the evolutionary and genetic relationships between species. Much of Linnaeus’ system was removed or altered, in fact, except for the kingdom Animalia.

Linnaeus’ scientific legacy lies most of all in his introduction of a hierarchical system of biological classification, as well as the use of binomial nomenclature.

Linnaeus received a medical degree in the Netherlands in 1735 and began work on the publication of his taxonomical system. It was called Systema Naturae, and it grew each year as he collected more specimens of organisms and as new ones were sent to him from scientists all over the world.

By the time Linnaeus published the 10th edition of his book in 1758, he had classified approximately 4,400 animal species and 7,700 plant species. Each species was identified by two names, much like a person’s first name and last name. Before Linnaeus’ classification system, it was not uncommon for a species’ scientific name to have eight parts.

Linnaeus simplified this by utilizing binomial nomenclature, which simply means a two-name system.

This naming technique works in concert with a hierarchical structure that goes from broad to specific, just like the taxonomical structure still in use today. At the top was the broadest level, and with each descending level, the divisions became more specific, until at the very bottom, individual species were left.

Linnaeus’ levels of taxonomy, beginning at the top, were:

• Kingdom.
• Class.
• Order.
• Genus.
• Species.

In some cases, Linnaeus further divided species into taxa, which were unnamed. His hierarchical classification system can be arranged in an upside-down phylogenetic tree, rather than Aristotle’s ladder. The tree provides a visual representation of how different species are related to each other, and what their most recent common ancestor is.

Any given organism’s species, genus, and every other position all the way to the top of the taxonomic hierarchy can be determined by name. The genus name is first, and the species name is second. Once you know those two things, you can figure out the rest. This remains true with modern classification.

Linnaeus is widely considered one of science’s heroes because his taxonomical framework is used to categorize and document all of life on Earth. Most people, however, have forgotten one aspect of his taxonomy because it is no longer in use, even though it was as hateful and harmful as other elements of his work were helpful and enlightening.

Linnaeus was the first to develop and publish a proposed division of humans into different races, which he called taxa (subspecies). He based these divisions on their geographic location, skin color and his perception of stereotypical behaviors.

In his book Systema Naturae, Linnaeus first describes Homo sapiens, and then breaks the genus Homo down further into four taxa:

• Homo Europeanus.
• Homo Americanus (referring to Native Americans).
• Homo Asiaticus.
• Homo Africanus.

Linnaeus describes each by their skin tone and supposed behaviors. Homo Europeanus, the species and taxon to which he himself belonged as a Swedish man, was described as “white, gentle and inventive,” according to the New World Encyclopedia. The descriptions for the rest of the taxa bear negative connotations.

Many adjustments have been made to the Linnaean classification system over time as scientists have made discoveries about fossils, DNA sequencing and molecular biology, among others. Linnaeus focused mostly on the physical characteristics of species, which is considered insufficient now.

As scientists have discovered new species and evolutionary history has come into sharper focus, many levels have been added to the Linnaean system of classification, such as phylum, superclass, subclass, family and tribe. Regardless of the level, when a group of organisms is being described, they are now called a taxon, or taxa for plural groups.

Most recently, a level called domain was added to the top of the hierarchy above kingdom. The three domains are Archaea, Bacteria and Eukarya. The four kingdoms Protista, Animalia, Fungi and Plantae fit within the Eukarya domain.

Although Linnaeus provided a framework for classifying living creatures, his own system was not limited to organisms. For instance, in his quest to classify the natural world, he created a kingdom of minerals. He also created a scientific name for Homo anthropomorpha, a proposed species that included all human-like mythical creatures, which he believed truly existed. These included the satyr, phoenix and hydra.