Darwin’s finches : The islands situated near the mainlands usually possess flora and fauna related to those of mainland. However, they have a unique diversity of species despite being related. One such example is Galapagos islands (Spanish Galapago – Giant Tortoise). Darwin visited the island in 1835 and described them as living laboratory of evolution. The islands have 26 species of birds and 11 species of tortoises. Out of 26 species of birds, 23 are endemic or found only in the islands. Amongst them were species of sparrow-like small black birds called finches. They are called Galapagos finches or Darwin’s finches (Lack, 1947).

They resemble mainland finches in plumage, body plan and short tails but differ amongst themselves as well as from mainland finches in shape and size of beaks, food habits, colour of feathers and body size. Thirteen species of finches occur in Galapagos island and one species in nearby Cocos island. Six species are of ground finches (Geospiza species), six species of tree finches (Camarhyncus species) and two types of warbler finches (Certhidia and Pinarolaxis species). The ancestors of Galapagos finches must have come from mainland.

They were seed eating. However, environment and availability of food on the various islands were different from those of the mainland. As a result variations appeared in them to suit their habitats. They ultimately produced the different species of finches, some of which evolved insect eating patterns. Divergence of organisms of a common stock due to adaptive changes to suit new environmental conditions is called adaptive radiation.