Analogy means similarity between 2 things. Analogous organs are also termed analogues. If any two structures or organs perform similar functions but are structurally different, they are analogous structures or analogous organs. Opposite of analogous organs are homologous organs. Homologous organs are the organs that are structurally similar to each other but perform different functions. Analogous organs and homologous organs also play an essential role in the evolution of species as both types are involved in different kinds of development. Examples of analogous organs are the wings of insects, birds, etc., which perform the same function of flying but are anatomically distinct from one another.
Analogous Organs
Analogous organs are the organs that are different anatomically in structure but perform the same function. They are involved in convergent evolution. Convergent evolution is a form of evolution where other species evolve independently to develop to achieve a similar type of function. In terms of cladistics, the biological classification of the convergent evolution phenomenon is homoplasy. The analogous organs belong to different, unrelated species, and due to evolutionary changes, the structures of the unrelated species develop in a certain way independently to perform similar types of functions. Generally, organisms that grow to have analogous organs do not share any common ancestor.
Examples of Analogous Organs
Wings of Bats, Birds and Butterflies
This organ presents the three different organisms that perform the same flying function but are different in structure. In birds, the wing structure is formed of bones covered with feathers. The wings of insects are nothing but the extension of the integuments, which is the outermost layer of any animal that protects the body. In bats, the wings are simply the folded skin of their fingers.
Sweet Potato and Potato
These plant parts are nothing but storage forms of starch and plant products, but anatomically, both are different from one another. Sweet potato is a modified root that performs the function of storing starch for the plants. A potato is simply a modified stem that also performs the function of storing starch for the plant.
Octopus and Mammal Eye
The organ is used to view the outer world for the organism, but structurally, they are both different. The difference is the procedure to consider the environment by focusing on the light. For mammals, the lens changes shape with the help of ciliary muscle to focus on light. For an octopus, the position of the lens is changed to focus on the object. That is, the lens of an octopus can move close or far from the direction of the object to focus on it.
Penguin and Dolphin Flippers
Dolphins walk on land; hence, they have evolved from mammals, whereas penguins can still fly and seem to be developed from birds. Both have flippers as the organ that helps them swim in the water.
Firethorn and Barberry
Both the plants have spines for protecting them. The stem is modified into thorns in firethorns, and in barberry, the leaves are modified into thorns.
Homologous Organs
Homologous organs are the organs that are structurally similar but still perform different functions. They are the result of divergent evolution. In divergent evolution, species are closely related to the same ancestors but develop similar structures that perform various tasks under different environmental conditions.
Examples of Homologous Organs
Vertebrate Forelimb
Most vertebrates like dogs, humans, cats, etc., are structurally similar but perform different functions. The whale uses flippers for swimming while humans, dogs and cats use their limbs to walk. Birds have wings that are used for flying.
The Pelvis of Snakes and Vertebrates
Dogs, cats, etc., have a pelvis similar to snakes. Nevertheless, it is used as a vestigial organ.
Leaves of Plants like Cactus, Pitcher Plant and Venus Flytrap
The leaves of all these plants belong to a common ancestor but perform different functions. Like the cactus leaves are modified to reduce water loss, whereas the leaves of Venus flytrap are modified to trap insects to derive nitrogen from them for the plant’s growth.
Mouthparts of Different Insects
Mouthparts of different insects like butterflies, grasshoppers and mosquitoes are structurally similar but perform other functions. The mouthparts of butterflies are used to suck nectar, the grasshoppers use their mouthparts to bite, and mosquitoes use their mouthparts to suck blood.
Conclusion
Analogous organs are different in structure but perform the same function. Organisms that develop to have analogous organs do not have any common ancestor. They are involved in convergent evolution, a form of development where different species evolve independently to grow to perform a similar function. The analogous organs belong to other, unrelated species. Homologous organs are structurally similar organs but still perform different functions. They result from divergent evolution in which species are closely related to the same ancestors but develop similar structures under other environmental conditions that perform different functions even after having the same structure.