What are Homologous Structures?
Those structures which are inherited from a common ancestor are called homologous structures. The word homologous is derived from two Greek words ‘Homos’ means same and ‘logos’ means relation, that is, having the same relation. Homologous structures are the similar characters in different organisms because of their inheritance from a common ancestor. These are the structures which have similar morphology, embryology and anatomy etc. but are dissimilar in their functions. In contrast to analogy or analogous structures, which are the structures in different species performing the same function, have similar appearance and structure but are not evolved together; therefore do not share a common ancestor.
The more closely the organisms are related the more common will be the homologous structures between them.
Examples of Homologous Structures
The most discussed example of homologous structures is the structure of forelimbs of different vertebrates, for example, arm of a human, flipper of a whale, the leg of a dog and wing of a bat. Although their structures are similar but they perform different functions. The arm of a human is for grasping, leg of a dog for walking, the wing of a bat for flight.
Othe examples of homology include the pelvis of a dog, cat, human and a snake. The leaves of a pitcher plant, a cactus, and a Venus fly trap are also examples of homology. Although all these now have different shapes and perform different functions but they all share a common ancestor.