How did Darwin explain adaptive radiation by taking an example of finches ?

Question

(a) How did Darwin explain adaptive radiation by taking an example of finches ?
(b) How did Darwin’s view on evolution differ from that of de-Vries ?

Answer 1

a) Darwin conjectured that the birds evolved on the island itself There were seed-eating features and other altered beaks arose allowing different types of food eating habits like insectivorous and vegetarian finches  This process of evolution of different species in a given geographical area starting from a point and radiating to other areas of (geographical) habitats is called adaptive radiation

(b) Darwin	de Vries
(i) Minor variation (heritable) cause evolution	Mutation caused evolution
(ii) Variation are small and directional	Mutation are random and directionless
(iii) Evolution is gradual	Single step large mutation / saltation causes speciation