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SAI International School
                                                   Subject- Biology
                                         Chapter- Heredity And Evolution
                  Subtopic- Evolution, Natural selection, Genetic Drift, Acquired and
                                                    inherited traits
                                                       Module-25
                                                     Lesson Notes


               EVOLUTION
                     Evolution is the sequence of gradual changes which takes place in the primitive
                       organisms, over millions of years, in which new species are produced.
               Case-1: Natural Selection:
               Situation 1 : • Colour variation arises during reproduction
                     All beetles red except one that is green → Crows feed on red beetle → No. of
                       beetles reduces

                     One beetle green → Progeny beetles green → Crows could not feed on green
                       beetles as they got camouflaged (hide) in green bushes → Number of green
                       beetles increases.

               Conclusion

               → Green beetles got the survival advantage or they were naturally selected as they
               were not visible in green bushes.
                 This natural selection is exerted by crows resulting in adaptations in the
                    beetles to fit better in their environment.





























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