(a) Homologous organs: These organs are similar in form (or are embryologically same), but perform different functions in different organisms. These organs provide strong evidence in the favour of evolution. For example, the bone structure observed in the forelimbs of birds and bats, flippers of dolphins and arms of human beings are similar and have the same pentadactyl plan but they perform different functions.
(b) Analogous organs: These organs have different origin and different basic structure but perform same function. For example, wings of birds and wings of insects; wings of birds and wings of bats (bird wings are made of feathers while bat wings are the folds of skin) have different structure but perform same function of flying. Thus, these organs provide evidence for evolution that they are different in origin but evolve to perform same function to survive in hostile environmental conditions.

(c) Fossils: They are the impressions of dead organisms and they can tell a great deal about the changes that various species of organisms have gone through. For example, Archaeopteryx is a connecting link between birds and reptiles and it suggests that the present animals have evolved from the existing ones through the process of continuous evolution.
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