Explain the interpretation of Charles Darwin when he observed a variety of small black birds on Galapagos Island ?
 

Biogeographical evidences suggests that the species restricted in widely separated region show similarity of ancestry.

Habitat isolation had probably restricted these organisms to a particular geography on the earth.

- This can be explained with the help of following processes.

$\Rightarrow \quad$ Adaptive Radiation : The process of evolution of different species starting from a point in a geographical area and finally radiating to other area of geography (habitats) is called adaptive radiation.

Example of adaption radiation are :

$(i)$ Darwin's Finches : Darwin observed an amazing diversity of creatures in Galapagos island.

There he saw the small black birds that amazed him the most later called as Darwin finches.

They represent one of the best examples of adaptive radiation.

He observed that there were many varieties of

finches in the same island and all the varieties have evolved on the island itself from original seed eating finches.

He explained that after originating from a common ancestral seed eating stock the finches must have radiated to different geographical areas and under gene adaptive changes, especially in the type of beaks.

Therefore, due to the alterations in beaks gradually, some become insectivorous and some vegetarian.

Living in isolation for long the new kind of finches emerged that could function and survive in new habitat.