Explain evolution by stages through the example of eye.

Explanation

The eyes are very important and complex sense organ for animals. The eyes cannot be produced by a single change occurring in the structure of DNA.
After a descent of several generations the eyes are formed in a gradual manner. The first eyes evolved in aquatic flatworms (Planaria) are simple eye-spots to detect light. Such rudimentary structure in flatworm provide survival advantage to the animal.

`rarr` Eyes in insects, octopus, other invertebrates and all vertebrates including human beings, have different structure and also have separate evolutionary origin.
`rarr` Eyes show development in accordance with adaptation.
`rarr` The complex structure of eye in higher animals has been created in stages over many generations.