Morphological and anatomical evidences of evolution, Biology

MORPHOLOGICAL AND ANATOMICAL EVIDENCES -

(i) HOMOLOGOUS ORGANS -

  • The organs apparently similar or dissimilar in structure and function, but of similar embryonic origin. Term homology used by Richard Owen 1804 - 1892.
  • A detailed and extensive study showes that all of them have following characteristics.
  • A fundamental similar plan
  • Contain approximately the same 'number of bones

1056_homologous organs.png

  • e.g. Fore limbs of whale, birds, bat, horse & man.
  • Mouth parts of insect is mode up of Maxilla, mandible, Labium, Labrum and hypopharynx but are adopted for different mode of feeding.
  • When function are different then it is called divergent evolution.

(ii) ANALOGOUS ORGANS -

  • The organs that have the same function and have superficial resemblance to one another but are dissimilar structure details and origin.
  • The phenomena among widely different groups is called convergent evolution.
  • e.g. Wings in insects, birds and bats are dissimilar in structure but similar in function i.e. flying.

(iii) VESTIGIAL ORGANS -

  • The organs that are present in reduced form and are useless to the possessor but correspond to the functional organs of related past animals.
  • e.g. Appendix, muscles of pinnae, nictitating membrane, coccyx, canine teeth and third molar in man, the rudimentary pelvic girdle in python.
  • In human beings total 180 vestigial organs are known.

382_vestigial rgans.png

(iv) ATAVISM (Reversal) -

  • It is the reappearance of certain ancestral characters that had either disappeared or reduced.
  • Example. Power of moving pinna in some person, greatly developed canine teeth, exceptionally long dense hairs (Lionboy of Russia), short tail in some babies, presence of additional mammae in some individuals.
Posted Date: 10/8/2012 9:24:45 AM | Location : United States







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