Evidence from comparative anatomy of evolution - Homologous organ, Homology

 

According to the concept of evolution animals adapt  themselves according to the different  environmental conditions. Due to this environmental condition, animals acquired some special characteristics to survive and reproduce in such environmental conditions. These special characteristics are called adaptations. 

These special characteristics are modification of those characteristic that are present in their ancestors. Therefore there are slight dissimilarities between the characteristics of closely related species but they have an original set of characteristics with these dissimilarities. The embryonic origin,  development, relationship as well as blood and the nerve supply of the such organ and organ system are quite similar in related forms. 

The basic similarities between similar and dissimilar organs is called homology. The organ showing homology is called homologous. 

Homologous  organs may be defined as the organs that are dissimilar in function but similar in embryonic origin  and development and having similar relationship with adjacent organs and similar  blood and the nerve supply. 

Birds and bats belong to different classes of vertebrates but their wings are quite dissimilar in structure.These  are homologous organs  with similar embryonic development, similar skeletal support and similar blood and the nerve supplies. This similarities is  because  the wing in both cases for the modification of forelimb but they have similar basic structure in their limb as were present in their ancestor.

During the long course of  evolution the forelimbs are  modified not only in the wing  of birth but also modified in the bat for flying. A number of other modifications can also be seen. These are modified into flipper of whale and seal and paddle of the penguin for the swimming, for fast running leg of horse and deer, hand  of man for grasping things but they have their  common  basic  structure in their forelimb

The homology  is not only present in the forelimb of vertebrates  but also present in most of the other organs of different categories of the vertebrates. This proves that  all vertebrates have  evolved from a common ancestor. It is called monophyletic origin.

The class insecta  of arthropods   is a largest  group of the animal kingdom. The mouthparts of insects are adapted for licking in houseflies, cutting in ants, chewing  in cockroaches, sucking in mosquitoes etc. But they have common mouth parts like labium,maxillae, labrum and hypopharynx with basically similar structural patterns.

Similarly the legs of insects are variously adapted for walking, jumping, walking, swimming, clinging etc  however they have common five basic segments like coxa, trochanter, femur, tibia, and tarsus.

Since homologous organ are found in organism and show adaptive radiation from  common ancestor so these organs show divergent evolution