Question

Which of the following is a pair of analogous organs?
A) Wing of the bird and flipper of whale
B) Fore limbs of horse and man
C) Wing of bird and forelimb of horse
D) Wing of insect and wing of bird

Answer 1

Hint: Comparative study of the morphology and anatomy of different groups of animals or plants reveals that certain structural features are basically similar. In vertebrates, the vertebral column has the same structural plan in different groups and limbs of the different tetrapod group are built on the same pentadactyl plan.

Complete answer:
Before discussing analogous organs, we have to check some basic points.
The degree of resemblance between two organisms of two different groups indicate how closely related they are in terms of evolution. Groups with very few common features are assumed to have diverged from a common ancestor much earlier in geological history than groups which have many common features. Based on structure, function and evolutionary status, three groups of organs can be recognized, namely homologous, analogous and vestigial organs.

Homology is the structural similarity and functional diversity between the adult organs of different groups. S, homologous organs are the structurally similar but functionally different adult organs of different taxonomic groups. The phenomenon by which a homologous structure gets specialized for different functions in the different groups is called adaptive radiation. The gradual diversification of organisms through adaptive radiation is known as divergent evolution. Eg: pentadactyl limb in vertebrates. It is clearly seen in forelimbs of mammals. In monkeys’ forelimbs are elongated for grasping, climbing and swinging. In horses, forelimbs are adapted to support the body and running. In whales, forelimbs have become flippers for steering and balancing during swimming.

Analogy is the functional similarity and structural diversity between the adult organs of different groups. So, analogous organs are the functionally similar but structurally different organs of different groups. Under similar environmental conditions, fundamentally different structures in different groups of organisms may undergo similar modifications to serve similar functions. This phenomenon is called convergent evolution or parallel adaptation. Examples for analogous structures are the wings of bats, birds and insects, the jointed legs of insects and vertebrates, the tail fin of fish, whale and lobster etc.

Vestigial organs are the highly degenerate or underdeveloped and apparently functionless organs that are smaller and simpler than the corresponding organs in ancestral species. Eg: halteres of flies and mosquitoes, vermiform appendix, nictitating membrane, wisdom tooth, body hair, ear muscles of human beings.

Here, the correct answer is (D) Wing of insect and wing of bird.

Note:The theory of organic evolution is perhaps the most reasonable explanation to account for the astonishing diversity of life on earth. At the same time, absolute proofs in support of it are lacking. Even then, it is built on a solid scientific foundation which is strengthened by convincing circumstantial evidence.