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What are the pieces of evidence of organic evolution? How comparative anatomy and embryology of animals give evidence of organic evolution?

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According to the concept of organic evolution, the present day animals and plants have been evolved by a process of gradual change in the earlier simple forms of life, which took place in millions of years. Following are evidence of organic evolution:-
  1. Palaeontological Evidence (Evidence from Fossil Record).
  2. Missing Links (Transitional Forms): The fossil organisms which show char­acters of two different groups are called missing links. Examples: Archaeopteryx.
  3. Comparative Anatomy and Morphology: There are similarities and differences among organisms of today and those existed years ago.
  4. Comparative embryology of organisms.
  5. Biogeographical Evidence (Evidence from Biogeography): Biogeography is the study of the distribution of animals and plants on this earth. The evidence of evolution based on biogeography are called biogeographical evidence.

Comparative studies of the embryology show great similarity in different groups of plants and animals.Embryos of all multicellular animals develop from a single cell (zygote) and all pass through a common series of stages, such as blastula, gastrula, and so on. The nearer the relationship of the adult structures, the greater is the similarity in the courses of embryo development. The embryos of fishes, reptiles, birds and mammals are all alike in the early stage of development.
Comparative anatomy gives another evidence of organic evolution. The different systems of the animal body are similar in many groups of organisms, e.g., nervous sys­tem, blood vascular system, respiratory system, excretory system, etc. The respiratory system of terrestrial vertebrates has two lungs, a trachea, a larynx, nasal chambers and nostrils. Likewise, the blood vascular system of all vertebrates contains a heart, ar­teries, veins and lymph vessels.
Despite the broad similarity, the organ systems of various groups have a varying degree of specialization according to the habitat and scale of evolution. Vestigial organs, homologous organs are other examples of anatomical evidence.

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