Question

Which of the following is an example of homology?
A. Dorsal fins of sharks and dolphins
B. Feathers of different bird species
C. Walking on two legs in birds and humans
D. Wings in birds and bats

Answer 1

Hint: When two structures are similar in morphology or genetic sequence and are derived from a common origin or ancestor, it is said to be homology and the structures are known as homologous structures. Homologous organs or structures generally result due to divergent evolution.

Complete answer:
Option (a) is incorrect. Dorsal fins of sharks and dolphins are analogous structures. Sharks are cartilaginous fishes, whereas dolphins are cetacean mammals. These two groups are related, but distantly. The evolution of fins in both the species is due to the habitat they share, that is water. The structures have evolved independently under environmental influences. Thus, this is an example of convergent evolution and the structures are analogous.
Option (b) is correct. Feathers of different birds are homologous structures. This is because all the birds have originated from a common ancestor and perform the same function. Thus, it is an example of homology.
Option (c) is incorrect. Walking on two legs is a form of locomotion, generally seen mammals. It is also seen in certain birds. Bipedalism in humans and birds is not derived from a common two-legged ancestor, but they have adapted to this form of locomotion at different times in evolution. It is thus a convergent form of evolution.
Option (d) is incorrect. Wings in birds and bats are analogous structures. This is because both the structures, though superficially similar, are of different evolutionary origins and thus not derived from a common ancestor. It is under similar environmental conditions they dwell in led to evolution of the wings in birds and the wing like patagium in bats.

Hence, the correct answer is option (B).

Note: Homologous structures are derived from common ancestors. It may or may not always serve similar functions. For example, the forelimbs of dogs, crocodiles, and flippers of whales are homologous because they are derived from a common tetrapod ancestor. In contrast, analogous structures, though superficially similar and have similar functions are not of the same evolutionary origin.