The taxonomic categories They comprise a series of ranges that allow organic beings to be organized hierarchically. These categories include domain, kingdom, phylum, class, order, family, genus, and species. In some cases, there are intermediate categories between the main.
The process of classifying living beings consists of analyzing the way in which certain informative characters are distributed among organisms, in order to be able to group them into species, species into genera, these into families, and so on..
However, there are drawbacks related to the value of the characters used for grouping and what is to be reflected in the final classification.
Currently there are about 1.5 million species that have been described. Biologists estimate that the number could easily exceed 3 million. Some researchers believe that the estimate exceeds 10 million.
With this overwhelming diversity, it is important to have a classification system that gives the necessary order to the apparent chaos.
Sorting and classifying seems to be an innate human need. Since we were children we try to group the objects that we see based on their characteristics, and we form groups of the most similar.
Similarly, in everyday life, we constantly observe the results of a logical ordering. For example, we see that in the super market the products are grouped into categories, and we see that the elements most similar to each other are found together.
The same tendency can be extrapolated to the classification of organic beings. Since time immemorial, man has tried to put an end to the biological chaos caused by the classification of more than 1.5 million organisms.
Historically, morphological characteristics were used to establish groups. However, with the development of new technologies, it is possible to analyze other characters, such as molecular ones..
On multiple occasions, the terms taxonomy and systematics are used wrongly, or even synonymously.
The taxonomy aims to simplify and order organisms in a coherent way into units called taxa, giving them names that are widely accepted and whose members share characteristics in common. In other words, taxonomy is responsible for naming organisms.
Taxonomy is part of a larger science, called systematics. This branch of knowledge seeks to classify species and study biological diversity, describing it and interpreting the results..
Both sciences seek the same objective: to reflect the evolutionary history of living beings in an arrangement that is a reproduction of this.
The classification is responsible for synthesizing a great variety of characters, whether morphological, molecular, ecological or ethological. Biological classification seeks to integrate these characters into a phylogenetic framework.
In this way, phylogeny is the basis for classification. Although it seems to be a logical thought, it is a subject debated by many biologists.
In accordance with the above, the classification is usually divided into phylogenetic or evolutionary, depending mainly on whether or not they accept paraphyletic groups..
Classification schools arise from the need to have objective criteria to assign the existence of a new taxon and the relationships between existing taxa.
Linnaean school: it was one of the first criteria used and there was no phylogenetic component. Morphological resemblance was the focus of this school, and such resemblance was not intended to reflect the evolutionary history of the group..
Phenetic school: It arises in the mid-60s and uses a classification "for convenience", since, according to its defenders, it is not possible to know with certainty the correct phylogeny.
Thus, as many characters as possible are measured and grouped for similarity. Using mathematical tools, characters are converted into dendograms.
Cladist school: proposed by the entomologist Hennig in the 1950s, it seeks the reconstruction of the phylogeny using the characters derived by the method of phylogenetic systematics or, as it is known today, cladistics. Currently, it is the most popular method.
Unlike the phenetic school, the cladist does give an evolutionary value to the characters that are included in the analysis. It is taken into account if the character is primitive or derived, taking into account an external group and assigning polarity and other properties to the characters.
In the taxonomy, eight basic categories are handled: domain, kingdom, phylum, class, order, family, genus, and species. The intermediate divisions between each category are used frequently, such as the subphyla, or the subspecies.
As we move down the hierarchy, the number of individuals in the group decreases, and the similarities between the organisms that form it increase. In some organisms, the term division is used preferentially, and not phylum, as is the case with bacteria and plants..
Each group in this hierarchy is known as a taxon, plural taxa, and each one has a particular rank and name, such as class Mammalia or genus Homo.
Organic beings that have certain basic characteristics in common are grouped in the same kingdom. For example, all multicellular organisms that contain chlorophyll are grouped in the plant kingdom.
Thus, organisms are grouped in a hierarchical and orderly manner with other similar groups in the aforementioned categories..
For biologists, the concept of species is fundamental. In nature, living things appear as discrete entities. Thanks to the discontinuities that we observe - either in terms of coloration, size, or other characteristics of the organisms - they allow the inclusion of certain forms in the species category..
The concept of species represents the basis of studies of diversity and evolution. Although it is widely used, there is no definition that is universally accepted and that fits all forms of life that exist..
The term comes from the Latin root species and it means "set of things to which the same definition is appropriate".
Currently, more than two dozen concepts are handled. Most of them differ in very few respects and are little used. For this reason we will describe the most relevant for biologists:
Typological concept: used since the time of Linnaeus. It is considered that, if an individual conforms sufficiently to a series of essential characteristics, a particular species is designated. This concept does not consider evolutionary aspects.
Biological concept: it is the most used and widely accepted by biologists. It was proposed by the ornithologist E. Mayr, in 1942, and we can state them as follows: "species are groups of current or potentially reproductive populations that are reproductively isolated from other similar groups."
Phylogenetic concept: was stated by Cracraft in 1987 and proposes that species are "The smallest cluster of organisms, within which there is a parental pattern of ancestor and descendant, and that is diagnostically distinct from other similar clusters."
Evolutionary concept: In 1961, Simpson defined a species as: "A lineage (an ancestor-descendant sequence of populations) that evolves separately from others and with its own role and trends in evolution."
Unlike the other taxonomic categories, species have a binomial or binary nomenclature. Formally, this system was proposed by the naturalist Carlos Linneo
As the term "binomial" indicates, the scientific name of organisms is made up of two elements: the genus name and the specific epithet. Similarly, we could think that each species has its first and last name.
For example, our species is called Homo sapiens. Homo corresponds to gender, and is capitalized, while sapiens is the specific epithet and the first letter is lowercase. Scientific names are in Latin, so they must be italicized or underlined.
In a text, when the full scientific name is mentioned once, the successive nominations will be found as the initial of the genus followed by the epithet. In the case of Homo sapiens, will be H. sapiens.
We humans belong to the animal kingdom, to the phylum Chordata, to the class Mammalia, to the order Primates, to the family Homidae, to the genus Homo and to the species Homo sapiens.
In the same way, each organism can be classified using these categories. For example, the earthworm belongs to the animal kingdom, to the phylum Annelida, to the class Oligochaeta, to the order Terricolae, to the family Lumbricidae, to the genus Lumbricus and finally to the species Lumbricus terrestris.
Establishing a coherent and orderly classification is vital in the biological sciences. Around the world, each culture establishes a common name for the different species that are common within the locality..
Assigning common names can be very useful to refer to a certain species of animal or plant within the community. However, each culture or region will assign a different name to each organism. Therefore, when communicating with each other, there will be problems.
To solve this problem, the system provides an easy and orderly way to call the organisms, allowing effective communication between two people whose common name of the animal or plant in question is different..