Classification

Classification is the process of organising organisms into groups based on their shared characteristics. These groups are known as taxonomic ranks.
It is a fundamental aspect of understanding biodiversity, enabling scientists to organise and understand the relationships between diverse life forms.
The modern system of classification follows the Binomial Nomenclature introduced by Carl Linnaeus, which is universal and uses Latin or Latinised names.

Classification is based on a hierarchical system which goes from broad to specific, starting with Kingdom at the top and then Phylum, Class, Order, Family, Genus, and Species at the bottom.
The acronym ‘King Phillip Came Over For Great Steak’ is often used to remember these levels.
Each level or rank in this hierarchy is called a taxon (plural: taxa).

The most specific rank, species, is a group of organisms that can successfully interbreed to produce fertile offspring.
Each species is given a unique two-part Latinised name, a binomial name, where the first part is the Genus (always capitalised) and the second part is the species (always in lowercase).
Both parts combined give the full species name, such as Homo sapiens (human beings). This name is always italicized or underlined.

Robert Whittaker introduced the first widely accepted Five Kingdom System that includes Prokaryotae, Protoctista, Fungi, Plantae, and Animalia.
However, this classification system has now been superseded by the three-domain system.

The Three Domain System, proposed by Carl Woese, is currently the most accepted model of classification. It divides organisms into three domains: Bacteria, Archaea, and Eukarya.
Bacteria and Archaea comprise all prokaryotic organisms (organisms without cell nuclei), while Eukarya includes all eukaryotic organisms (organisms with cell nuclei).
The first two domains consist of unicellular organisms, whereas the Eukarya domain contains complex multicellular organisms and single-celled protoctists.

Phylogenetics is the study of the evolutionary relationships between different species, showing the evolutionary ‘branches’ that link organisms.
It plays a crucial role in classification because it provides a basis for organising species based on their evolutionary relatedness.
Phylogenetic trees, also called evolutionary trees or cladograms, visually represent these relationships between species. The points where branches meet, or ‘nodes’, represent the common ancestor of the species in the branches that follow. This can illustrate when species diverged from common ancestors.