Animals and principles of classification,keeping in view historical

There is a large collectionof very dissimilar forms of organisms,found on Earth.Over 1.5 million types of animals and over 0.5 million types of plants are know to biologists and these are only a small percentage of the total types estimated to live on Earth. Organisms range in complexity from small and simple bacteria to large and complex human beings.Some of them live in sea,some on land some walk,others fly,and still others are stationary.Each has its own way of life i.e.getting food,avoiding unfavourable envirnomental conditions,finding a place to live,and reproducing its kind. When we realize that there are so many diverse kinds of organisms,it becomes clear that no one can lesrn about the way of life of each. To study such a large collection,biologist classify the organisms into groups and subgroups for this task they require some system.Biological classification is a method by which biologists group and categorize species of organisms.

AIMS OF CLASSIFICATION

The branch of biology which deals with the classification is called taxonomy and the branch which deals with classification and also traces the evolutionary history of organisms is known as systematics.

The main aims of both these branches are;

To determine similarities and difference among organisms so that they can be studied easily.
To find the evolutionary relationships among organisms.

Basis of classification

Classification is based on relationship amongst organisms and such relationship is got through similarity in form or structure.These similarities suggest that all organisms are related to one another at some point in their evolutionary histories.However,some organisms are more closely related than other.For example sparrows are more closely related to pigeons than to the insects.It means that the former two have common evolutionary histories.

Biollogists have classified all the known organisms into groups and subgroups on the basis of similarieies.These similarities are seen in structures,biochemistry,cytology and genetics.Modern genetics provides an other type of imformation to taxonomists.The genetic differences between two studied organisms can be determined and can be used for getting idea about similarities and differences in their structures and functions.

Animals and principles of classification,keeping in view historical