During his visit to Galapagos Island, Darwin observed that there were many varieties of small black birds in these islands which differed mainly in the beak shape and feeding habits.
After analysing them, he realised that they were evolved on the same island itself. He conjectured that from the original seed-eating birds, other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography is called adaptive radiation.
