Evolution is a sequence of gradual changes from simple to complex life forms. Many organs adapt to new functions as a result of evolution.
Homologous organs are those that have a similar basic structure and embryonic origin but carry out different functions in various species. Divergent evolution leads to homologous structures. Homology suggests a common ancestry.
Example, the forelimbs of a frog, a lizard, a bird and a human being show similarities in basic structure. However, these organs perform entirely different functions.
The given figures show homologous organs :
A lizard’s forelimbs are modified for creeping movements, a bird’s forelimbs are modified for flying, and a human’s forelimbs are used for grasping. A frog’s forelimbs assist the animal in supporting the front end of the body while at rest and also serve as shock absorbers when the animal leaps and lands on the ground. The basic resemblance between these various vertebrates’ forelimbs suggests that all vertebrates share a common ancestor, meaning that they all developed from a common ancestor who had “five digited” or “pentadactyl” limbs (the basic plan of limbs).
This means that during evolution, these animals have changed in response to the unique requirements of the succeeding generations.