Homologous organs are those organs which are similar in origin but different in function. It represents a case of divergent evolution. The presence of a structure or physiological process in an ancestral organism, which has become greatly modied in more specialized, apparently related organisms , may be interpreted as indicating a process of descent by modication. In this case the function of organs diversied and became different from the common ancestor.
Analogous structures are those which are different in origin but similar in function. The existence of analogous structures suggest the occurrence of convergent evolution. It may be explained in terms of the environment, acting through the agency of natural selection, favouring those variations which confer increased survival and reproductive potential on those organisms which possess them. In this case different organs with different origins start performing similar functions and differ from their ancestral trait. With the help of fossils we can know the morphological details of the organisms in the past and can relate them to the organisms in the present to understand the process of evolution. We can also trace the time at which the organism existed.
