Question

Provide a DETAILED response and describe an example of homologous structures to demonstrate how organisms are closely related, be sure to discuss similarities, differences, and how they came to be.

Answer 1

The structures in different organisms which have similarity in their anatomy or basic plan but serve different functions are known as homologous structures. This similarity in their anatomy is due to the phenomenon of common ancestry. These organs have the similar basic structures and developmental origin. A common example of homologous structures is found in the forelimbs of vertebrates like whales, bat, cheetah and human.

The pattern or arrangement of bones of forelimbs in whales, bat, cheetah and human provides detailed explanation of homology. Whales, bat, cheetah and human, all these organisms are the different species opf the same class Mammalia. The anatomy of their forelimbs reveals similar (but not same) anatomical structures, i.e, all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in hteir forelimbs. But the functions of forelimbs in these animals show clear dissimilarities. In case of human, the forelimbs is used for holding the objects while it is used for running, swimming and flying in case of cheetah, whale and bat respectively. The pentadactyl limb is the characteristic for all these animals and it is the ancestral terrestrial vertebrate limb plan which is subsequently adapted by modification for different uses or habitats. The forelimbs in all these animals developed along different directions due to adaptations to different needs. This is called divergent evolution because originwise common structure diverged towards different directions to perform different functions according to the need of the organism. Hence, homologous structures are the result of divergent evolution.