(a) How do the following provide evidences in favour of evolution in organisms? Explain with an example for each.

(i) Homologous organs

(ii) Analogous organs

(iii) Fossils

(b) Explain two methods to determine the age of fossils.




(i) Homologous organs - They are organs that are similar in structure and have the same origin but have been modified to perform different functions.


Wings of birds and forelimbs of humans perform different functions but they have similar skeletal structure because they have the same origin ie., they have evolved from a common ancestor.

(ii) Analogous organs - They are organs that are dissimilar in structure and do not have the same origin but perform similar functions.

Example: Wings of bats and birds have different structures but they perform the same function ie., flying . So, they do not show common ancestry but trace evolution due to which they became capable of flying.

(iii) Fossils - The remains of dead animals or plants that lived in the remote past are known as fossils .

They provide information about prehistoric organisms.


Archaeopteryx had feathered wings like those of birds and tail like those of reptiles . Archaeopteryx is therefore a connecting link between birds and reptiles and hence suggest that birds have evolved from reptiles


Two methods for determining age of fossils are:

  • Carbon dating - By detecting the ratios of different isotopes of the same element in the fossil material. 
  • Relative method - If we dig into the earth and start finding fossils, it can be assumed that the fossils closer to the surface are more recent to those found in the deeper layers.


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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo