What is taxonomy?

Taxonomy definition

The definition for taxonomy is that it’s the study and classification of living and extinct forms of life. It divides all of life into groups known as taxa, where a single taxon represents a particular way of dividing up nature – for example, a population of whales or a species of fish.

Under the most widely used system of biological classification, known as the Linnean system, every taxon is then put into a hierarchy based on its taxonomic rank. The lowest level of ranking is normally the species, though lower ranks, such as subspecies, can be used in certain situations.

Closely related species form a genus, which are put together into larger and more distantly related groups of organisms until they reach domains, the top rank.

The traditional three domains of taxonomy are:

• Eukarya, which contains animals, plants, fungi and almost all multicellular life.
• Bacteria, which is a vast group of mainly single-celled organisms.
• Archaea, which are a distinct group of organisms once considered bacteria, but now known to be their own form of life.

More recent evidence, using genetic and molecular data, has shown that Eukarya might actually be descended from Archaea. As a result, a two-domain taxonomic system, containing just Bacteria and Archaea in the top tier, is becoming increasingly accepted by scientists.

What is a taxonomist?

Taxonomists are scientists that work out how different groups of life are related, with famous early examples including John Ray and Daniel Solander. Many taxonomists attempting to understand the natural world work today in institutions such as the Natural History Museum.

One of these scientists is Dr Gavin Broad, who looks after the insect collections we care for. He’s classified many different organisms during his career, a process that begins with a scientific description.

“To build a taxonomy, you first need to note down all of the unique characteristics of an organism that set it apart from all others,” Gavin explains. “This can include physical characteristics such as its colour and size as well as less obvious features like its genetics.”

“I would use these characteristics to build up an identification key, so that the differences between this organism and its relatives can be highlighted. It can sometimes be difficult to distinguish a species from its closest relatives, or sister taxa, so it’s important to be as detailed as possible.”

By comparing an organism with its relatives, a researcher can work out whether it’s an existing species or one that’s new to science. If it’s new to science, a taxonomist will need to designate a type specimen – a single specimen that other scientists can use to compare any other individuals or specimens against.

They also need to give this new species a name, making use of a system that dates back to 1700s and the botanist Carl Linnaeus, who’s widely considered the pioneer of modern taxonomy.

Linnaean classification

Carl Linnaeus, also known as Carl von Linné, was an eighteenth-century Swedish scientist who’s often known as the ‘father of taxonomy’. Having developed a passion for plants at a young age, he would go on to revolutionise the science of classification.

As a botanist, Carl Linnaeus would have been used to the long, formal Latin descriptions used to name plants. The tomato, for instance, was given the name Solanum caule inermi herbaceo, foliis pinnatis incisis, racemis simplicibus, which means “the herbaceous nightshade with a smooth stem which has incised pinnate leaves and a simple raceme”.

With European empires spreading across the world, more and more plants were being sent back to scientists to be named. This made it increasingly difficult to use the inconsistent and long Latin descriptions as names for the different species.

Carl Linnaeus’s classification system changed all this by simplifying how species are named. His new naming system, known as binomial nomenclature, gave every species a two-part name. While some scientists had used similar systems in the past, this was the first time it was formalised and used consistently.

As a result, the scientific name of the tomato became the much shorter Solanum lycopersicum. The first part of the name is the genus, while the second is the name of the species.

Scientific texts may also add the name of the person who first named the species, who’s known as the authority. In this case, a tomato would be known as Solanum lycopersicum Linnaeus. Adding this information means that later scientists can more easily track a species back to the original publication it was described in.

These binomial names are sometimes known as Latin names. This is because, like most scientists at the time, Carl Linnaeus published his work in Latin. This even extended to his own name, which was Latinised to Carolus Linnaeus.

Carl Linnaeus’s naming system was originally published in 1735, and he continually revised and updated it for more than 20 years. His most important works were published in the 1750s, with Species Plantarum and the tenth edition of Systema Naturae jointly considered the beginning of modern taxonomy.

By identifying the characteristics of different plants and animals, Carl Linnaeus named around 12,000 species. Not all of these names are still in use today. The name given to the kraken, Microcosmus marinus, has fallen out of fashion because it’s now recognised as a mythical creature rather than a species of squid.

Other taxa, meanwhile, have been renamed or reclassified. For example, Carl Linnaeus’s classification of a rabbit as Lepus cuniculus has been changed to Oryctolagus cuniculus.

Dr Gemma Bramley, a taxonomist from Royal Botanic Gardens, Kew, explains that these changes take place because taxonomy is constantly evolving as new discoveries are made.

“Fundamentally, taxonomy is a structure we’re trying to place onto nature because without it we couldn’t organise our thoughts and knowledge about the world,” says Gemma. “It’s a system that’s been built over hundreds of years by many different people who all have different ideas.”

“As a result, all taxa, and taxonomy, are abstract to some degree. As our understanding of the world changes, we have to adjust our ideas to better fit the facts.”

How are taxonomy and phylogeny different?

Taxonomy and phylogeny are two closely related terms that are sometimes mistakenly used interchangeably. While taxonomy is the study of how organisms are classified, a phylogeny – sometimes known as a phylogenetic tree, evolutionary tree or tree of life – is a diagram used to represent the relationships between organisms.

The two concepts often go hand in hand. Taxonomy provides the names for different species, while a phylogeny shows how they’re related. This has particularly been the case since Charles Darwin and Alfred Russel Wallace published their theory of evolution by natural selection.

In the 1859 edition of On the Origin of Species, Charles Darwin included a phylogeny to help explain his ideas. While other scientists had previously published similar diagrams, Charles Darwin’s was widely seen and helped to popularise phylogenies.

Scientists could now start to investigate evolutionary relationships, and adjust taxonomies accordingly, but they were still limited to comparing the physical characteristics of different groups. It would take until the twentieth century, when the concepts of genetics, mathematics and evolution were combined, for researchers to get a better idea of how all life is related.

This led to the growth of phylogenetics, which is defined as the study of evolutionary relationships between different organisms. Scientists can now use similarities in DNA, proteins and other parts of the body to work out how related different taxa are and to build phylogenetic trees.

Some researchers now even group different taxa based on molecular data alone, putting them into what’s known as an operational taxonomic unit. Most scientists, however, say that DNA and protein data should be used alongside other characteristics to describe groups of organisms.

With more accurate information about how organisms are related, taxonomy has also changed. One major change is that taxonomists now try to only name monophyletic taxa, which contain an organism and all of its descendants.

This has challenged groups originally based on appearance alone. Reptiles, for example, aren’t monophyletic because birds are treated as a different group, even though they descend from them.

Even though taxonomy keeps shifting, with new and conflicting evidence emerging all the time, it’s crucial that we try to categorise the natural world. Without it, nature would be much harder to understand.

Why is taxonomy important?

Taxonomy is important because it ultimately forms the foundation of all biology. If different species and groups weren’t consistently named, no one would be able to accurately discuss what taxa they were talking about.

While this would cause immediate issues for scientists studying these organisms, it would also have an impact on our everyday lives. Taxonomy allows researchers to quickly find out the relatives of certain species, which has consequences for everything from disease control to drug development.

Galantamine, for instance, is a drug used in the treatment of Alzheimer’s disease. It’s naturally produced by snowdrops, but only in small amounts. By examining relatives of the snowdrop, scientists found that daffodils produce galantamine in larger quantities, making them a more useful way to source the drug from nature.

“Taxonomy is also vital for food security,” Gemma adds. “A team at Kew have been looking for wild relatives of coffee that will be more resilient to climate change. If we didn’t know how these species were related, and the places they grow, we wouldn’t be able to make these connections.”

Taxonomy isn’t just for living organisms, either. For example, the relationships between different dinosaurs can tell us about how they might have lived, while human taxonomy can give clues about where we come from.

Despite the importance of taxonomy, it doesn’t always receive the recognition it deserves. Less funding is now directed towards pure taxonomy, meaning that there are fewer taxonomists than there used to be.

This is particularly problematic in the face of the ongoing mass extinction of life on Earth, when naming new organisms is vital. Species can’t be protected if no one knows they exist, and laws to protect biodiversity don’t work unless they can accurately identify the taxa involved.

Promoting the work of taxonomists and making the collections cared for by us and other organisations more available is essential to combatting the biodiversity crisis. Their work provides both a record of life on Earth and a guide to help save it.