History of classification and its need

Introduction:

Classification of organisms based on their similarities and dissimilarities is required for studying organisms.
 

History of classification:
 

Artificial system of classification:

• These classifications are based on morphological characteristics, which is a system of artificial classification.
• The drawback of this system is that completely related species are grouped differently.
• While completely unrelated species are classified together within the same groups.
• Example: The animals that have wings are classified together, therefore bats, birds and insects were put together in the same group.

350 BC - Aristotle

• He classified plants and animals based on their morphological characteristics and habitats.
• He classified animals into two categories - enaima [with red blood] and anaima [without red blood].
• He also classified animals based on their habitat as aquatic [example: fish, whale], terrestrial [example: reptiles, cattle] and aerial [example: birds, bat].
• He divided plants into three groups: herbs, shrubs and trees.

23 - 79 AD - Pliny and Elder

• They classified animals into flight and non-flight. For example, bats, birds and insects were classified as flight animals.

Linnaeus:

• He classified plants into 24 classes based on the numerical strength of sexual charecters as monandria, diandria, polyandria etc.

Natural system of classification:

• In the natural system of classification along with morphological characteristics several other characters such as cytological, physiological, biochemistry etc. are also utilized.
• There is only a little chance of placing unrelated organisms in the same group.
• It is the most widely used system of classification.

1862 - 1863 : Bentham and Hooker

• They made a natural system of classification in the book ‘Genera plantarum’.

Phylogenetic system of classification

• This system of classification is based on the evolutionary relationship between organisms.
• The phylogenetic system of classification is highly dynamic, and fossil records are the major source of information.
• This classification is always changing with the identification of new fossils.

1887 - 1890 : Engler and Prantl

• They proposed the first phylogenetic system of classification.
• They arranged flowering plants based on increasing complexity of floral morphology; monocots were considered as primitive to dicots.

1959 - Hutchinson and 1966 - Takhtajan:

• They proposed the improved phylogenetic system of classification. The relationship was based on evolution.

Types of classification:

Linnaeus: Two kingdom classification
1866 - Haeckal - Three kingdom classification
1956 - Copeland - Four kingdom classification
1969 - Whittaker - Five kingdom classification
1990 - Carl Woese - Six Kingdom classification or three domains system
The Linnaean two-kingdom system was followed up until 1969.
Whittaker's five kingdom classification was adopted in 1969.
 

Need for classification:

1. When the information about a group of organisms is known then every organism in the group need not be studied separately.
2. Classification is required for identifying the organisms.
3. The characteristics of organisms can be studied even if they are not present in a locality.
4. Studying extinct organisms requires classification.
5. Evolutionary tendencies can be known from the relationship between numbers of various taxa.

Frequently Asked Questions - FAQs

Q1. What are the two kingdoms of the Two-kingdom system of classification?
Ans: Kingdom Plantae, Kingdom Animalia

2. What is the difference between three kingdom system and three domain system?
Ans: