Homologous Organs are those organs of various animals that have similar basic structures but perform different functions. Homologous Organs provide evidence for the evolution of organisms. These organs can be used as an example of Divergent Evolution in which the organisms have common ancestors but later on, due to the development of differences, result in the establishment of different species. These species may have some similar morphological characteristics as their ancestors which can be linked back to them having a common ancestor but due to the different ecological niches now, these species have evolved into performing different functions from one another. Therefore when related organisms evolve completely different biological characteristics, it is called as Divergent Evolution.
This type of evolution of two or more animals in which they have a common ancestor, and hence similar anatomy of their body parts/organs, but have different ecological niches resulting in their different functions are called as Divergent evolution and these types of organs are called as Homologous Organs.
Definition Of Homologous Organs
‘Homologous Organs can be defined as the organs of different animals that are similar in structure but perform different functions. Homologous organisms share a common ancestry.’
The word Homologous is derived from two Greek words, ‘Homo’ and ‘Logos’. Homo means same and Logos means relations. Therefore the literal meaning of the word Homologous means having the same relations. Therefore the organs of different organisms having the same relations but different functions are called homologous organs.
Examples of Homologous Organs
Forelimbs of Vertebrates
The basic structure of the forelimbs of almost all the vertebrates like dogs, humans, whales (flippers), frogs, cats, birds etc are similar but they perform different functions. For example, the flippers of whales are used for swimming, humans use their limbs for writing, grasping, birds use their wings for flying, dogs and cats use their forelimbs for walking etc.
The similarity in their structure is evidence of the Divergent Evolution which reflects that the vertebrates have been evolved from a common ancestor.
Pelvis Present in Snakes
The pelvis of dogs, cats and humans are shared by primitive snakes like pythons as a vestigial organ. This is an example of Homologous organs as well as points towards the common ancestry of snakes with humans and dogs.
Leaves of Cactus, Pitcher plant, Venus flytrap and poinsettia
All these three plants have different leave functions but these are an example of homology because they belong to a common ancestor.
Mouthparts of Various Insects
Mouthparts of insects like the butterfly, grasshoppers, mosquitoes, honey bee etc have a similar basic structure but perform very different functions and hence are an example of Homologous Organs. For example, butterfly sucks nectar, grasshoppers mainly bite and chew and mosquitoes suck the blood.
Ear ossicles of Tetrapods and Bones in Jaw Fish
The ear ossicles of a group of vertebrates including amphibians, reptiles, birds, and mammals (stapes, incus, and malleus) are homologous to the parts of fish jaws and gill arches. Tetrapods include all the land vertebrates and the former land vertebrates that have now adopted the aquatic life.