The Concept of Classification
Have you ever visited a library? How are the books arranged and kept?
Are they arranged randomly or systematically? Obviously the books are arranged systematically in the shelves.
Science books are kept separately in their respective shelves. Science books are kept separately from social or commercial books. Biology books are separated from physics books or chemistry books.
Likewise, in the shop, laboratory or pharmacy items are sorted and placed on the basis of their similarities.
In the world, there are numerous varieties of living organisms.These organisms do vary in size, structure, shape, habitat, mode of feeding and even mode of reproduction.
In the world, there are numerous varieties of living organisms.These organisms do vary in size, structure, shape, habitat, mode of feeding and even mode of reproduction.
The organisms can be sorted out and placed into different groups based on their similarities. The system of sorting out and placing organisms into different groups on the basis of their similarities and differences is called classification.
1.Artificial classification
2.Natural classification
Linnaeus included all worm-like organisms in a single group, the vermes. This included wide a range of animals as from nematodes, earthworms to snakes. This was an artificial classification since it did not consider natural relationships such as the fact that snakes have backbones and earthworms do not have. Thus, snakes have more features in common with vertebrates than with worms.
Bats and birds would be placed in the same group because all have the ability to fly since they posses wings. But bats share many features with mammals. They have features like hair, mammary glands, sweat glands and different types of teeth which are characteristics of mammals. Therefore, bats are more related to mammals than birds.
Characteristic features which show homology are distinguished from those which show analogy. Example the fore limbs of mammals, whales, birds and bats have the same basic pattern and similar bone arrangement, i.e. homologous. This suggests that these organisms are coming from the same ancestor and that can be placed in the same group.
The wings of birds and grasshoppers are analogous. The wings of birds have internal skeletons while the wings of grasshoppers do not have bones but they perform similar function. These organisms cannot be placed in the same group since they are different in many ways.
2.It does not take much time to classify organisms based on this system (not time consuming).
3.It does not need expertise (even a layman can do).
4.It is relatively stable i.e. not easily changing from time to time.
2.Different or unrelated organisms may be placed in the same group e.g. bats placed in a group of birds, worms placed with snakes in the same group
3.The system does not provide enough information about its members.
4.It is difficult to incorporate additional information.
2.It reflects evolutionary relationships.
3.Unrelated organisms cannot be placed in the same group.
4.It makes it easy to incorporate additional information.
2.It requires expertise i.e. more knowledge about an organism.
3.It is time consuming.
4.It is relatively unstable i.e. it changes from time to time.
5.It is more expensive since more data are required.
Differences between natural classification and artificial classification
The Importance of Classifying Living Things
The following are importances;
1.Classification makes the study of living things easy
2.Classification makes communication easy among biologists from different parts of the world
3.It provides good organized system in which a newly identified organism can be easily fitted in future.
4.It makes it easier to identify organisms
5.It can be used to predict characteristics that are present in the members of the same group.
1.Classification makes the study of living things easy
2.Classification makes communication easy among biologists from different parts of the world
3.It provides good organized system in which a newly identified organism can be easily fitted in future.
4.It makes it easier to identify organisms
5.It can be used to predict characteristics that are present in the members of the same group.
Types of Classification Systems and Their Differences
There are two types of classification1.Artificial classification
2.Natural classification
- Artificial classification
Linnaeus included all worm-like organisms in a single group, the vermes. This included wide a range of animals as from nematodes, earthworms to snakes. This was an artificial classification since it did not consider natural relationships such as the fact that snakes have backbones and earthworms do not have. Thus, snakes have more features in common with vertebrates than with worms.
Bats and birds would be placed in the same group because all have the ability to fly since they posses wings. But bats share many features with mammals. They have features like hair, mammary glands, sweat glands and different types of teeth which are characteristics of mammals. Therefore, bats are more related to mammals than birds.
- Natural system of classification
Characteristic features which show homology are distinguished from those which show analogy. Example the fore limbs of mammals, whales, birds and bats have the same basic pattern and similar bone arrangement, i.e. homologous. This suggests that these organisms are coming from the same ancestor and that can be placed in the same group.
The wings of birds and grasshoppers are analogous. The wings of birds have internal skeletons while the wings of grasshoppers do not have bones but they perform similar function. These organisms cannot be placed in the same group since they are different in many ways.
Merits and Demerits of Each Type of Classification System
- Advantages of artificial system of classification
2.It does not take much time to classify organisms based on this system (not time consuming).
3.It does not need expertise (even a layman can do).
4.It is relatively stable i.e. not easily changing from time to time.
- Disadvantages of artificial system of classification
2.Different or unrelated organisms may be placed in the same group e.g. bats placed in a group of birds, worms placed with snakes in the same group
3.The system does not provide enough information about its members.
4.It is difficult to incorporate additional information.
- Advantages of natural system of classification
2.It reflects evolutionary relationships.
3.Unrelated organisms cannot be placed in the same group.
4.It makes it easy to incorporate additional information.
- Disadvantages of natural system of classification
2.It requires expertise i.e. more knowledge about an organism.
3.It is time consuming.
4.It is relatively unstable i.e. it changes from time to time.
5.It is more expensive since more data are required.
Differences between natural classification and artificial classification
| Artificial classification | Natural classification |
|---|---|
| (i) Considers few features in common | Considers many features in common |
| (ii) Does not reflect on evolutionary relationships | Reflects on evolutionary relationships |
| (iii) It is easy to classify | It is difficult to classify |
| (iv) Not time consuming | It is time consuming |
| (v) Does not require expertise | Requires expertise |
| (vi) New information cannot be added | New information can be added |
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