Provide evidence in favour of evolution in the following organisms. Explain with an example for each.

(i)  Homologous organs

(ii)  Analogous organs

(iii)  Fossils

(b) Describe two techniques for estimating the age of fossils.

(a)   (i) Homologous organs: They are organs that are similar in structure but have been modified to perform different functions. For example, the forelimbs of humans, frogs and lizards have similar structures. Frog uses it to hop, and as a shock absorber, human use it to write, hold etc. and lizard use it to creep on walls.

(ii)  Analogous organs have different structures and appearances but perform similar functions. For example, the wings of bats and birds have different structures but perform the function of flying. They do not show common but trace evolution, due to which they became capable of flying.

(iii)  Fossils are the remains of plants and animals found under the earth that lived in the past. They tell us about the evolutionary relationships in the past. For example, Archaeopteryx was a traditional form between birds and reptiles.

(b)  Fossils can be determined by:

(i)   Carbon - 14 Dating: All organisms have some percentage of carbon, while it decreases as we die. The percentage of fossils is compared with the present percentage of living organisms to determine their age.

(ii)  Relative method: The earth is dug, and the fossils found close to the earth are recent, whereas the ones found in deeper layers are older.