Question

Explain with an example for each, how the following provides evidences in favour of evolution in organisms.
(a) Homologous organs
(b) Analogous organs
(c) Fossils

Answer 1

a) Homologous organs are those organs which have the same structure and embryonic origin but perform the different functions. For example, forelimbs of whale, bat, deer, rabbit have the same structure but are modified in different ways to perform locomotion in different ways. Such kind of structures give rise to divergent evolution.

b) Analogous organs are those organs which have the different embryonic origin but perform the similar function. For example, wings of a bird and wings of the insect. Wings of bird are modified forelimbs while wings of an insect thin membranous expansion of exoskeleton. Analogous organs are formed due to convergent evolution.

c) Fossils are the remnants of the past organisms which get buried in sedimentary rocks. Different fossils are formed in the different aged rock sediments. The study of fossils existing in the different rock layers indicate the time period when they existed. Thus different life forms have been formed at different times in the history of the earth. Fossils indicate how the evolution took place leading to the formation of complex life forms from simple ones by the gradual process. For example, fossil bird Archaeopteryx is considered as a connecting link between reptiles and birds indicating that birds evolved from reptiles. It shows the presence of characters of both birds and reptiles like the presence of teeth, wing feathers, clawed toes and tail.