LINNAEAN TAXONOMY OF LIVING BEINGS - BIOLOGY - 2025

The Linnean taxonomy comprises a series of hierarchical categories and nested designated by the Swedish naturalist Carl Nilsson Linnaeus (1707-1778), better known as Carolus Linnaeus Linnaeus or simply to group the enormous diversity of living organisms.

Linnaeus' contributions to taxonomy are incredibly valuable. The system he devised to group organic beings is used today and is the basis of modern taxonomy.

Source: Alexander Roslin

Currently, the categories proposed by Linnaeus are still valid, although subcategories have been added to the list. Likewise, the way Linnaeus named the species, with a specific Latin genus and epithet, is still in use.

However, today the classification is in accordance with evolutionary thinking - practically non-existent in Linnaeus' time - and morphology is not the only characteristic used to group living beings.

What is taxonomy?

Before talking about the taxonomy proposed by Linnaeus, it is necessary to define what taxonomy is. This is the science that is responsible for creating the names for the various forms of life. It is part of a larger discipline, systematics.

The aim of systematics is to understand the evolutionary relationships that connect living organisms, interpreting their change and diversification over time. This distinction is important, as many students tend to use the terms vaguely, and sometimes synonymously.

Classification of organic beings

Classifying the various forms of life that inhabit the planet seems to be an intrinsic act of humanity since time immemorial. Understanding relationships and proposing reproducible and formal classifications of living beings were ideas that disturbed thinkers as old as Aristotle.

Classifying life forms seems to be as complex a task as defining life itself.

Biologists propose a series of properties that all living organisms share, with the conspicuous exception of viruses, which allows it to be separated from non-living matter, such as movement, growth, feeding, reproduction, metabolism, excretion, among others.

In this way, choosing the correct characteristics that will provide useful information to establish a classification system has been an open question since ancient times.

For example, going back to the example of Aristotle, he used to divide animals by their ability to lay eggs, the oviparous, or by the growth of young in the womb, the viviparous.

Aristotle did not use the features that he did not consider informative, he did not establish the classification system based on the number of legs, for example.

Linnaean thought

To understand Linnaeus, it is necessary to place ourselves in the historical context where this naturalist developed his ideas. Linnaeus' philosophical tendency was based on the fact that species were immutable entities in time, which were created by a certain divinity and have remained the same.

This thought was accompanied by a biblical vision, where all the species that Linnaeus and his colleagues observed, were the result of a single event of divine creation, as described in the book of Genesis.

However, there were other sources that encouraged this line of thinking. For the moment, the evidence for evolutionary change was ignored. In fact, the evidences of evolution that we take as obvious today were misinterpreted and were even used to refute change.

Linnaeus contributions

Linnaeus was given the task of classifying and logically identifying the various living things on the planet.

Division into kingdoms and taxonomic ranges

This naturalist divided living creatures into two main kingdoms; animals and plants - or Animalia and Plantae.

Following this initial division, he proposed a classification hierarchy consisting of six ranks or categories: species, genus, class order, and kingdom. Note how each category is nested in the upper range.

Since Linnaeus's works date from the 18th century, the only way to assign living beings to the proposed categories was by observing morphology. In other words, the taxonomic relationships were inferred by observing the shape of the leaves, the color of the fur, the internal organs, among others.

Binomial system

One of Linnaeus' most notable contributions was the implementation of a binomial system for naming species. This consisted of a Latin name with a specific genus and epithet - analogous to the "name" and "surname" of each species.

As the names are in Latin, they must be reported in italics or underlined, in addition to that the gender begins with a capital letter and the specific epithet with a lowercase letter. AND

It would be incorrect to refer to our species Homo sapiens as homo sapiens (no italics) or Homo Sapiens (both capitalized).

Changes to Linnaean taxonomy

Over time, Linnaean taxonomy changed, thanks to two main factors: the development of evolutionary ideas thanks to the British naturalist Charles Darwin and, more recently, the development of modern techniques.

Evolutionary thinking

Evolutionary thinking gave a new nuance to the Linnaean classification. Now, the classification system could be interpreted in a context of evolutionary relationships and not in a merely descriptive context.

On the other hand, currently more than six taxonomic ranges are handled. In certain cases, intermediate categories such as subspecies, tribe, subfamily, among others, are added.

Modern techniques

In the mid-nineteenth century it became clear that a classification divided only into the animal and plant kingdoms was inadequate to catalog all forms of life.

A crucial event was the development of the microscope, which was able to distinguish between eukaryotic and prokaryotic cells. This classification managed to expand the kingdoms, until Whittaker in 1963 proposed the five kingdoms: Monera, Protistas, Fungi, Plantae and Animalia.

The new methodologies allowed the in-depth study of physiological, embryological and biochemical characteristics, which managed to confirm - or in some cases refute - the arrangement proposed by morphological characteristics.

Today modern taxonomists use very sophisticated tools, such as DNA sequencing, to reconstruct the phylogenetic relationships between organisms and propose a suitable classification system.

References

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