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Organic evolution is the study which deals with gradual change of living organisms either at once or periodic of time in order to adapt his/her environment. The major evidence which support the theory of organic evolution includes:-

(a) Evidence from fossil record: Fossil is the remain of plants and animals of past found in the sedimentary rock. The study of fossil is called PALAENTOLOGY.The study of rock show that dug deeper in the sedimentary rock are more like primitive form of life and those in upper layer are the modern form of life.This study of fossil show that organism remain fixed, they rather change through come from simple to more complex.

(b) Evidence from comparative embryology: Embryology is the study which deals with development of embryo. Comparative embryo show that in certain stage of embryonic development of same group of animal are very similar and distinguishable, indicating that those organisms arose frame the common ancestor. For example the embryo of fish ,mammal and birds are similar in earlier embryonic stage ,they all appear fish like because all posses gill shits ,gills two heart chamber and tail are disappear.

(c) Evidence from comparative anatomy: Anatomy is the study structure and form of organs in the body of living organism. The basic structure similarities and different among the group of living organism indicate the closely relationship among them. Some resemblance among organism assumes that these organisms come from same ancestor and the structural modification is due to the environment and genetically changes.

(d) Evidence from comparative physiology: Physiology is the study of function of an organism. The evidence from comparative physiology that body function resembles from other organism. For example Removal of thyroid gland in tad pole in order to prevent metamorphosis can continue. Due to these functions of thyroid gland from cattle which take place in the body of tadpole indicate that change had occurred.

(e) Evidence from Vestigial structure: Vestigial structure are those structure present in the organism but reduced in one group and well developed in other group of organism . For example Tail and ear muscles these structure are to day and much reduced respectively in man but well developed in other Animal such as cattle, dog, donkey etc. Also Appendix in man it is much reduced because has no function but well adapted in rabbit because has an important function.

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