Arxiu d'etiquetes: taxonomical categories

Where do names of species come from?

All known living beings have names that allow us to recognize and classify them. However, only scientific names are valid for scientific purposes. Who does assign these names? Has it been always done the same way? And the most important: is there any rule when assigning a name to an organism?

Previously in All you need is Biology, we talked you about classification and phylogeny of organisms. Now, we bring you the answers to all these questions about nomenclature and taxonomy. Keep reading and you will discover some curiosities!  

The value of scientific names

If someone asks us what a dog or a cat is, of course all of us will know the answer. However, these names are not useful from a scientific point of view (despite biologist use them assiduously), especially when making studies and publishing papers. Common names (such as ‘dog’ or ‘cat’) are not constant: every language, every country, even every region, has their own terms to refer to their organisms. Even sometimes they change through time or are used to appoint different organisms (e.g. the red panda, which is near to mustelids, and the giant panda, a bear, don’t belong to the same family despite being called pandas).

As you see, using only common names in science could put you in trouble. If someone publish that has performed a study about reproduction of macaw populations, we could not know of which species they are talking about; the common name of this bird varies among some countries; moreover, there exist different species of macaws. Thus, the study does not make sense without context.

So, the use of scientific names in science is very important: they are constant worldwide (we avoid translation problems) and refer only to one organism with no ambiguity.

Currently, designation of scientific names follows the binomial nomenclature, that is, a scientific name of a species is composed by two terms: the genus (an upper level of classification than the species) and the specific epithet or name (and not the species, as some people tend to confuse). While the first term has validity by its own, the second one only has it if is preceded by the genus.

Thus, and keeping with the example above, the macaws from this study actually belong to the genus Ara, but there are different related species of macaws belonging this genus (Ara ararauna, Ara glaucogularis, Ara militaris…).

Macaw of the species Ara ararauna. Picture by Ralph Daily, CC.

However, how has the way biologists assign names changed through the time?

Linné, the father of binomial nomenclature

For a long time, biologists have tried to classify and give names to every living being they discover. The science of defining and naming groups of organisms according to their shared features is known as taxonomy.

In the beginning, there was not a clear consensus for naming the species. For the first ‘taxonomists’ it was of a big importance to classify and identify poisonous and medical plants, of which there are ancient documents wrote by Egyptians more than 3000 years ago.

The first person who started to formally classify organisms was Aristotle (384-322 AC). He was the first to differentiate between animals and plants, besides starting the classification of organisms according to their ‘parts’: four legs, warm body, etc.

During the Middle Age and the beginning of the Modern Age, most of scientists followed the Aristotle’s system of classification. Thanks to the improving of observing tools, such as the development of the first optical lenses during XVI and XVII centuries, some biologists started to improve their descriptions, and eventually abandoned this system.

However, among taxonomist still didn’t exist a formal consensus for assigning names. Before the instauration of the binomial system, species were named with a term (the genus) followed by a specific epithet or name composed by one or more words which described the species. This system, known as polynomial system, gave room to really long names such as ‘Plantago foliis ovato-lanceolatus pubescentibus, spica cylindrica, scapo tereti‘. Of course, this was not an optimum system.

During XVI and XVII centuries, Caspar Bauhin made the firt steps to simplify this system, sometimes shortening species names to just two terms. However, it was the Swedish botanical Carl von Linné (or Carolus Linnaeus) who formalized the use of the binomial nomenclature in his publication Species Plantarum (1753). Since then, species were given a name composed only by two terms: the genus and a trivial name designated by its descriptor; e.g., Panthera tigris (tiger).

Carl von Linné. Public domain.

The establishment of this system was favored by three reasons:

  • Its economy: there are needed only two words to identify a species with no error.
  • Its diffusion and general use by scientists, who standardize them and promote their use.
  • Its stability: scientists try to preserve the original name of an organism even if its classification changes through time.

How to name an organism: the nomenclature codes

Taxonomy and nomenclature are two different but inseparable concepts. While taxonomy is the science of describing and classifying organisms, nomenclature is the tool that allows taxonomists to assign names to those organisms.

In 1758, Linné stated the basis for an objective classification of species in the 10th edition of one of his most famous publications, Sistema Naturae:

  • Each species must have an own scientific name, unique and universal.
  • When a species is given more than one name by different scientists, the oldest one must prevail.
  • Scientific names are composed by two Latin or Greek terms: the first one corresponds to the genus and the second one, to the species belonging this genus.
  • The first letter of the genus must be written in upper case, while the specific epithet or names must be written in lower case. Moreover, both terms must be written in italic or underlined.
Cover of the 10th edition of Sistema Naturae. Public Domain.

Nomenclature has been getting more and more complex over the years. Nowadays, there are international codes of nomenclature for every group of organisms, like the ICZN (International Code of Zoological Nomenclature) or the ICN (International Code of Nomenclature for algae, fungi, and plants), amongst others. Taxonomist from each branch must obey their own codes when naming an organism.

Two of the most important rules when giving a name are the validity and the availability of the name. Let’s imagine we discover a new species of wasp of the genus Polistes: in one hand, the name (Polistes x) must be available, that is, it must accomplish the needed requirements to be assigned to our species. These requirements are gathered in the international codes, which are based on the Linné’s criteria. Moreover, a name is available when it is accompanied by a formal (published) description. Availability of a name can change under certain circumstances; e.g., a name considered unavailable can be available again if is republished following the code’s criteria.

In the other hand, a name must be valid, that is, it must have not been used to designate another organism, or considered invalid. For example, two taxonomists one before the other describe the same species and give it different names; in this case, the valid name would be the oldest one, so the second one would become a junior synonym according to the priority principle, thus getting invalid for its use.

When giving names gets out of hand…or not

Usually, when giving name to a species taxonomists get inspired by specific features of the organism (Dosidicus gigas (giant squid)), its native location (Synergus mexicanus (gall wasp from Mexico)) or in honor to relatives or other scientists.

However, nomenclatural world is full of curiosities, from scientists that give extravagant names to their species to the ones that get inspired by their favorite characters or TV shows:

  • There exists a genus of moths called La (by Bleszynski, 1966). Its ambiguity with the feminine article ‘La’ in Spanish (‘the’ in English) makes search engines go crazy. Moreover, some of the species belonging this genus were given names like La cerveza, La cucaracha or La paloma (literally, ‘The beer’, ‘The cockroach’ and ‘The dove’ in Spanish, respectively).
  • While some taxonomists give species short names, others prefer them longer: Gammaracanthuskytodermogammarus, Rhodophthalmokytodermogammarus and Siemienkiewicziechinogammarus are genera of amphipods from the Baikal lake given by the naturalist Dybowski. For sure he had much fun with this!
  • During a long time, it was a common practice to use specific epithets and names to insult other scientists (e.g. stupidus). Fortunately, this is currently prohibited.
  • Abra cadabra, Aha ha, Attenborosaurus (dinosaur genus given after the naturalist David Attenborough), Acledra nazgul, Desmia mordor (in honor to the Lord of the Rings), amongst others.

It is important to note that the international codes try to avoid this kind of names; but it is still funny! If you haven’t had enough, take a look to this list. It will not disappoint you!

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Do you still think naming an organism is an easy task?


Main picture property of Irene Lobato Vila (author of this post) took at the Smithsonian’s National Museum of Natural History (Washington D.C., EUA).

Classification and phylogeny for beginners

In this blog, we usually use therms related with the classification of living beings and their phylogeny. Due to the difficulty of these therms, in this post we will explain them for those who are introducing to the topic. 


Before introducing in the topic, it is necessary to explain two concepts, which are usually confused: systematics and taxonomy.

Systematics is the science of the classification and reconstruction of phylogeny, it means that is responsible for reconstructing the origin and diversification of a taxon (unit that we want to classify, such as a species, a family or an order).

On the other hand, taxonomy is the study of the principles of scientific classification, the order and the name of organisms.

In other words, while systematics is responsible for creating systems of classification, which are represented by trees, taxonomy establishes the rules and methods to identify, name and classify each species in the different taxonomic categories based on systematics.


We cannot begin to talk about how to classify species without knowing what is a species and other classification levels of organisms.


Along history, it has been given several definitions to the concept species with different approaches.

  • Morphological concept of species: a species is a group of organisms with fix and essential features that represent a pattern or archetype. This concept is totally discarded nowadays, despite morphological features are used in guides to identify species.
Despite all guides use morphological features to identify species, morphological concept of species is not used (Picture: Revista Viva).
  • Biological concept of species: a species is a group of natural populations which reproduce among them and reproductively isolated and have their own niche in nature. So, a species has common ancestry and share traits of gradual variation.  This definition has some problems: it is only applicable in species with sexual reproduction and it is not applicable in extinct species.
  • Evolutionary concept of species: a species is a single lineage of ancestor-descendent populations that maintains its identity in front of other lineages and has its evolutionary tendencies and historical destination. This approach and the biological one are, in fact, complementary because they are talking about different phenomenons.
  • Phylogenetic concept of species: according to this point of view, a species is an irreducible group of organisms, diagnostically distinguishable from other similar groups and inside which there is a parental pattern of ancestry and descendants.  This point of view covers sexual and asexual reproduction.
According to the phylogenetic definition of species, A, B and C are different species. In the C group, all of them are the same species with different types (Picture: Sesbe).


Species are classified into a hierarchical system based on more taxonomical categories. From the highest to the lowest category, organisms can be classified in: Domain> Kingdom> Phylum> Class> Order> Family> Genus> Species> Subspecies> Variety> Form. 

We are giving an example: imagine dogs.  Dogs, like wolf, are included in the same species: Canis lupus, but dog is the subspecies Canis lupus familiaris. The naming of a species is its genus (Canis) followed by the specific epithet (lupus). The other taxonomical categories of dogs are: Eukarya Domain, Animal Kingdom, Chordata Phylum, Vertebrata Subphylum, Mammalia Class, Carnivora Order and Canidae Family.

Dogs and wolfs are included in the same species, but they are different subspecies (Picture: Marc Arenas Camps).


To reconstruct tree of life, it is the relationships between living and extinct species (phylogeny), we use traits. Traits are features of organisms that are used to study the variation inside a species and among them.

To reconstruct the phylogeny, it is used the shared traits among different taxa. We have to distinguish two types of similarity: when similarity of traits is a result of a common lineage is called homology, while when it is not the result of common ancestry is known as homoplasy.

Probably, it will be easier to understand it with an example. The wings of owls and quails are similar because they have the same origin (homology), but the wings of insects, birds and bats, despite they have the same function, they do not have the same origin (homoplasy).

The wings of insects, birds and bats are an homoplasy (Picture: Natureduca).

There are three types of homoplasy:

  • Parallelism: the ancestral condition of a variable trait (plesiomorphic) is present in the common ancestor, but the derived state (apomorphic) has evolved independently. An example is the development of a four-cavity heart in birds and mammals.
  • Convergence: in this case, the homoplastic trait is not present in the common ancestor. The structures originated by convergence are called analogy. An example is the wings of insects and birds.
  • Secondary loss or reversion: consist on the reversion of a trait to a state that looks ancestral. So, it looks and old state but, in fact, is derived.
paralelismo, convergencia, reversion
Biological parallelism, convergence and reversion (Picture: Marc Arenas Camps).

There are different types of traits that are used to order living beings: morphological, structural, embryological, palaeontological, ethological, ecological, biochemical and molecular.

Species that share derived states of a trait constitute clades and the trait is known as synapomorphy. Synapomorphies are traits that were originated in a common ancestor and are present in that ancestor and all its descendants. So, mammary glands are a synapomorphy of mammals.

Mammary glands are a synapomorphy of mammals (Picture: Tiempo de éxito).

After the selection of traits, the several classification schools use them in different ways to get the best relationship between living beings.


  • Notes of the subject Advanced Biology Basics, Degree in Biology (University of Barcelona).
  • Hickman, Roberts, Larson, l’Anson & Eisenhour (2006). Principios integrales de zoología. Ed. McGraw Hill (13 ed).
  • Izco (2004). Botánica. Ed. McGraw Hill (2 ed).
  • Shnek & Massarini (2008). Biología. Ed. Médica Panamericana (7 ed).
  • Vargas (2009). Glosario de Cladística: Introducción a la sistemática filogenética.
  • Cover picture: Tree of life mural, Kerry Darlington