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

• 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.

(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.