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EVOLUTION BY STAGES

                   1.  Evolution of eyes
                     Eyes are the organs of sight. Eyes are complex in vertebrates like humans.
                     They did not evolve all of a sudden, but evolved gradually.
                     In earlier forms of organisms like euglena, a small eye spot was seen hidden.


















                     Flatworms have eye spots to detect light. These eyespots gave survival
                       advantage to flatworms.
                     Gradually, with time, eyes developed. All vertebrates (mammals) have similar
                       basic structure of eye.
                     Evolution of complex organs is not sudden. It occurs due to minor changes in
                       DNA, however takes place bit by bit over generations.
                 Flat worm has rudimentary eyes. (Enough to give fitness advantage)
               • Insects have compound eyes.
               • Humans have binocular eyes.

                   2.  Evolution of feathers
                     Feathers evolved in dinosaurs for insulation against cold weather. Later, birds
                       adopted feathers for flight.
                     Example:
                  (i) Dinosaurs had feathers, but could not fly using feathers.
                  (ii) Birds seem to have later adapted the feathers to flight.

               ARTIFICIAL SELECTION

                     Process of selecting desired traits to breed other plants/animals to get desirable
                       traits is termed as Artificial selection.
                     Humans have been a powerful agent in modifying wild species to suit their own
                       requirement throughout ages by using artificial selection.
                     Example:
                     (i) From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale,
                       cabbage and kohlrabi were obtained by artificial selection.
                     (ii) Wheat (many varieties obtained due to artificial selection).


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