Biological Classification

‘We are all connected; To each other, biologically. To the earth, chemically. To the rest of the universe atomically.’ – Neil deGrasse Tyson

Scientific classification in biology or biological taxonomy is defined by Ernst Mayer as ‘The arrangement of entities in a hierarchical series of nested classes, in which similar or related classes at one hierarchical level are combined comprehensively into more inclusive classes at the next higher level.’

Biological classification is based on shared descent from the nearest common ancestor. The important attributes or traits for biological classification are ‘homologous’ i.e. inherited from common ancestors. These traits must be kept separate from those that are ‘analogous’.

Birds and bats both have the power of flight, but this similarity is not used to classify them into a class because it is not inherited from a common ancestor. In spite of all their differences both bats and whales feed their young with milk and this is one of the features that classifies them both as mammals, since it was inherited from a common ancestor.

It can be difficult to determine whether similarities are homologous or analogous. Until recently Golden moles, found in South Africa, were placed in the same taxon (insectivores) as North Hemisphere moles, on the basis of behavioural and morphological (form and structure). However, molecular analysis shows that they are not closely related, so their similarities are due to convergent evolution rather than shared descent, and so should not be used to place them in the same taxon.

biological classsification

In biological classification rank is the level in a taxonomic hierarchy. Examples of ranks are kingdom, phylum, class, and order. Each rank then has sub categories beneath it.

The basic ranks are species and genus. When an organism is given a species name it is assigned to a genus, and the genus name becomes part of the species name. Hence why the species name is also called the binomial – two-term name. For example, the zoological name for the human species is Homo sapiens. In this case Homo is the generic name and is capitalised; sapiens indicates the species and is not capitalised.

Human Example of Calssification

Domain: Eukarya

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Mammalia

Subclass: Theria

Order: Primates

Suborder: Haplorrhini

Family: Homininae

Genus: Homo

Species: Homo sapiens

I’m sure in the list above some of the terms are familiar, such as Vertebrata, meaning with a backbone and Mammalia. So without knowing you probably knew quite a few of the terms from Biological Classification.

It’s no secret that humans (or most of them anyway)  like to keep things organised. Garages, libraries, workshops and offices are easier to work in if there is a system in place to keep track of things. Biology is no exception. Its a lot easier to study things if we have a system that keeps some things apart from other things. Biologists call this taxonomy and after researching this topic further I can understand why this method of classification is such a common and successful means of classification.


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