CLASSIFICATION (TAXONOMY) OF LIVING THINGS | DON STEVE BLOG
March 29, 2024

There are over 2,000,000 known different organisms in the world today and probably over 1,000,000 are left to be discovered and named. All these living things have different characteristics such as shape, size, colour, and height. It will, therefore, be extremely difficult to study these millions of living things without arranging them into groups. Classification (taxonomy) helps to give a universal scientific name to every species so that students of different languages know the scientific name of that species. Common names vary from language to language while scientific names are internationally accepted.

Biologists, in arranging living things into groups have developed systems of using similarities to unite species into groups and using differences to separate groups. The science of arranging living things into groups based on structural, genetic or cellular organization is called classification or taxonomy. Examples of structural similarities and differences exist in fish, frog, lizard, bird and man. They are grouped together as vertebrates because they all possess backbones (vertebral column).

On the other hand they are grouped differently because frog has a moist and scaleless skin, fish has gills and fins, lizard has a dry scaly skin and tail, bird has beak and feathers while man has hair, mammary glands and three tiny bones (hammer, anvil and stapes) in the inner ear.

The relationship between organisms can also account for groupings. If two animals have the same number of similar chromosomes, then the two animals are closely related and can be grouped together. For example, Gorilla and Chimpanzee have 48 chromosomes each hence they are grouped into the family Pongidae. The same reason goes for cellular organization for grouping. For example, all animals with one cell are grouped as Protozoa (unicellular organisms) and those with more than one cell are grouped as Metazoa (multicellular organisms).

 

Taxonomic grouping

Living things are first separated into large

groups called kingdoms. The division of kingdoms into smaller groups is called phyla (singular: phylum). The term division rather than phylum is usually used for plants. Phyla are divided into smaller groups called classes. Each class is further divided into orders. Orders are further divided into families. Families are again divided into genera (singular: genus). A genus is broken into species.

  1. A species is a population of related organisms that can interbreed within themselves to produce fertile offspring.
  2. Thus a genus is a group of a closely related species.
  3. A family is a group of related genera.
  4. An order is a group of related families.
  5. A class is a group of related orders.
  6. A phylum is a group of related classes.
  7. A kingdom is a group of related phyla.

 

The system of naming living things (Nomenclature)

Scientifically, every living thing has two names. The first name is the genus (started with a capital letter) to which closely related species belong. Different species can belong to the genus just as the surname of our family is being shared with other members of the family.

The second name is the species (started with a small letter) to which the organism belongs. This name belongs to one kind of organism only. It does not share it with other members of the genus. The first and second names are also known as the generic and specific names respectively. For example Homo sapiens (man), Musca domestica (housefly), Ipomea batata (potato) and Hibiscus esculentus (okra).

Both the genus and species are written in italics or underlined. The system of giving two names to an organism is known as binomial nomenclature and it was developed by a Swedish botanist, Carl Linnaeus in the 18th century.

Carl Linnaeus (1707 – 1778) father of taxonomy

 

Sometimes we call living things their common names such as cat, dog, lion, rabbit and goat. These names are regarded as nicknames. These names are not definite as one common name can be used for so many organisms.

 

Major groups of living things

Living things are divided into two kingdoms – the Plantae (plants) and Animalia (animals) according to the old system of classification of Carl Linnaeus still being in use by some people.

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