(a) Homologus organs are defined as the organs which have same structure but different functions. For example: forelimbs of a man and a bird have same structure but they have different functions.
This presence of homologus organs provides evidence that they have derived from the same structure and have different functions.
(b) Analogous organs are the organs of organisms which have different structure of organs but have same functions. For example: wings of an insect and wings of a bird have different type of structure and performs same functions of flying.
Those organs, which have different basic structure but have similar appearance and perform similar functions are called analogous organs.
For example: The wings of an insect and a bird have different structure but they perform the same function of flying.
Analogus organs prove that the organism belonging to different ancestors performs similar functions and they keeps evolving with environment favorable conditions.
(iii) Fossils are defined as the dead remains of plants and animals that lived in remote past.
The remains of dead animal or plants that lived in the remote past are known as fossils.
The presence of fossils proves the evolution. The example of Fossil is: A bird Archaeopteryx has many characteristics of reptiles and seems to be evolved from reptiles.
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