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Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.

Species and taxonomy

This topic involves manipulation of words, hopefully in a constructive way.

A species is a grouping of organisms in which the members have similar characteristics to each other, and they can breed with each other to produce fertile offspring.

Classification is the process of arranging organisms into a series of categories according to shared characteristics, and phylogeny is the evolutionary development of diversity within groups of organisms. Systematics is also an attempt to categorise and record the diversity of living things and explain their evolutionary interrelationships over time. Cladistics is an approach that seeks to trace the development of present-day organisms from a group's most recent common ancestor, often expressed as a branching tree-like diagram (cladogram).
The plural of taxon is taxa

A taxon is the name of a group used in the process, and taxonomy involves naming an organism using this system.

This process fits any living (or extinct) organism into a set of groups, according to features of biological significance. Originally this was based on simple observable features including behaviour, but in recent years it has increasingly been based on biochemical differences. Protein structure is one area - especially antigens (which elucidate immunological reactions) - and details of DNA (both nuclear and mitochondrial) and ribosomal RNA, which can be obtained as a result of different genome sequencing techniques.

Each group has fewer members than the previous one, so the process of classifying an organism involves zooming in on an increasingly individual description of that organism in relation to other similar organisms. This effectively explains the relationship with others, underlining the significance of the evolution process.

This system is called a nested hierarchy. There are different ways of setting this out, and the following system is usually used at this level.

Groups within the standard phylogenetic classification system

domain
kingdom
phylum
class
order
family
genus
and species

[Other categories may be slotted in between these
e.g. suborder and infraorder between order and family, and of course sub-species below species
]


The bottom line (or two)

The final stage of classification, giving an organism a unique scientific name, consists of a double name - 'binomial' - including the genus and species names.
By convention, this is printed in (mostly lower case) italics, with only the genus name starting with a capital.
black-rat320 (22K)
The black rat
Rattus rattus
sprat320 (11K)
The sprat
Sprattus sprattus
Although this is sometimes called a 'Latin name', it is not always in Latin. It may be based on Greek, and often combined in a style which mimics normal or technical language. Often it does translate into a meaningful phrase which summarises the individual nature of the organism involved.

Another convention: It is permissible to abbreviate species names by shortening the genus name, e.g. the bacterium Escherichia coli can be subsequently referred to as E. coli, but it is wrong to assume that a reader (or listener) knows what species is being discussed. I recall one of my university lecturers getting himself confused when referring to the protozoan Entamoeba coli.

Species names are sometimes changed. Occasionally it is found that a species was described (and named) previously, so the oldest reference must take priority. Taxonomists may also split or combine taxonomic groups. Organisms may be moved into different groups if they are found to differ from other organisms in the group. Occasionally Latin name changes bring about small changes at the end of the words if a different gender is involved.

blue-tit320 (16K)
The blue tit
Cyanistes caeruleus
GreatTit320 (14K)
The great tit
Parus major
The well-known garden bird species the blue tit used to be named Parus caeruleus, in the same genus as the great tit Parus major. However since 2005 it has been renamed Cyanistes caeruleus on the basis of analysis of the mtDNA cytochrome b sequences [base sequence of mitochondrial DNA coding for the respiratory electron transport chain protein] which suggested Cyanistes was an earlier offshoot.
Both remain within the family Paridae. See the panel opposite.

As part of the naming process, it is conventional to deposit a (dead, preserved) specimen of the organism in a museum or herbarium, and to publish a description of it in a reputable scientific journal. Early examples were presented in a standard format: a Latin article referring to the organism as a species nova (new species). Part way down there was usually a paragraph which explained where the organism was found, and this was headed Habitat (It lives ..). Over time, this Latin verb became a noun in English with Biological significance.

Another linguistic note: at the genus level we are being general - i.e including other fairly similar organisms, whereas at the species level we are becoming specific - i.e. relating only to a single type of organism.

Putting names to all the categories

Methanosarcina Ecoli Yeast Amanita Amoeba Lumbricus
Drosophila melanogaster Marchantia Maize Dogrose Apple tree Dandelion
Sprat Dogfish Whale shark Midwife Toad boa constrictor Blue tit
Great tit Ruddy Duck black rat brown rat chimp320 (33K) Man
Click on the thumbnail images above for more information below:

blank (1K)
. .

domain    ..
kingdom  ..
phylum    ..
class         ..
order       ..
family      ..
genus       ..
species     ..

Common
name
         ..


The actual names for each category may be given in classical/Latin form or more everyday language:
e.g. Kingdom animalia (animals) - plantae (plants)
Some have a similar ending classical format: families ending -idae, etc.

Names behind the naming system
How many domains? How many kingdoms?

Some exam boards state that recall of different taxonomic systems, such as the three domain or five kingdom systems, will not be required, yet they expect candidates to be familiar with the standard phylogenetic classification system shown on the left.

Originally 'living things' were placed into either the Animal kingdom or the Plant kingdom.

Carl von Linné (Linnaeus) (1707–1778)
published a book Systema Naturae in 1735) in which he identified each organism with a snappy two-word description, rather than a rambling string of descriptions. He was a Swede, and like many academics of his day, he used quite a lot of Latin.
Each person naming a species is often referred to by an abbreviation, and so organisms named by Linnaeus himself often have their scientific name written with 'L.' or 'Linn.' afterwards.

Ernst Haeckel (1834-1919)
was a multi-talented German scientist who coined many terms used in Biology. He advocated the use of three kingdoms: plants , animals and protists (single celled organisms).

R.H. Whittaker (1920–1980)
was an American plant ecologist, specialising in plant community analysis, succession, and productivity. In 1969 he proposed the 5 Kingdom Classification :
Monera - primitive organisms - very small and single celled - prokaryotes (no true nucleus, nucleic acids unprotected): bacteria, archaebacteria, cyanobacteria and mycoplasma.
Protista (sometimes called Protoctista) - [mostly] single-celled eukaryotes (cells with a true nucleus), mainly aquatic, mostly marine and some photosynthetic: diatoms, algae, Euglena and protozoans like Amoeba, Paramecium, Plasmodium etc.
Fungi (Mycota) - eukaryotic, either as a simple network with branching structure - mycelium - built up from thread-like tubular structures called hyphae which may form into fruitbodies, or ovoid cells (yeasts) - mostly saprophytic or parasitic. Also includes lichens, mycorrhiza, etc.
Plantae (Metaphyta): eukaryotic (cells with a true nucleus and cell wall), autotrophic, multicellular organisms containing the pigment chlorophyll within chloroplasts, which enables them to carry out the process of photosynthesis. This kingdom includes a wide range of forms: herbs, shrubs, trees, flowering and non-flowering plants.
Animalia (Metazoa): eukaryotic (cells with a true nucleus and no cell wall), heterotrophic, multicellular organisms.

Lyn Margulis (1938–2011)
defended the five-kingdom system and proposed that in the evolution of life, eukaryotes developed after the uptake of prokaryotic organisms which eventually developed into organelles like mitochondria and chloroplasts within cells (endosymbiont theory).

Carl Woese (1928-2012)
in 1977 championed the three-domain system: archaea, bacteria, and eukaryote domains. This split the prokaryotes into two groups, Archaea (originally called Archaebacteria) and Bacteria (originally called Eubacteria). Archaea

Alternatively, or consequently, six kingdoms may be distinguished: Archaea , Bacteria , Protista, Fungi, Plants, Animals.

Other related topics on this site

(also accessible from the drop-down menu above)

Similar level
Evolution
Eukaryotic cells
Prokaryotic cells
Virus particles
Endosymbiont theory

Lower level - but attempting to show features of biological significance
Variety of life
Plant groups
Simple organisms
Invertebrate groups
Insects
Cold blooded vertebrates
Warm blooded vertebrates

Web references

Carl Linnaeus From Wikipedia, the free encyclopedia

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