Answer:
While on his voyage on the Beagle,while in Galapagos Island he observed that Finches(birds) across the island are similar but different in the structure of their beaks. This mystified him and he puzzled on thus on why there were differences in the beaks shapes.
He therefore postulated from the observation that beak shapes of these birds must be responsible for the adaptation to their habitats.Thus these birds must have come from common ancestors,(and the need to survive by adaptations to different environments is responsible for the beak shapes). The driving force for these phenomena is Natural selection.Therefore,where the size of beaks is the needed adaptation for survival,birds with larger sizes will be selected over those with smaller beaks for eating Feeds(selection pressure) and therefore will be better adapted and naturally selected than smaller birds.
Darwin predicted that the dormant traits(large beaks) will remain in the population as the parents pass these to their offspring from generation to generation,while the population smaller beaks which could not resist the selection pressure will fizzled out.
Thus the better adapted larger beak population will dominate and evolved after a long period of time.Thus all organisms with adaptations and naturally selected on earth must have evolved from a common ancestor.
Although Darwin proposed these,he lacks knowledge of genetics,therefore he could not explain how dominant traits for adaptation are inherited from one generation to another.However,mutation which gives rise to variations is driving force for the changes in structural characteristic for adaptation.Gene flow,gene drifts,together with natural selection are the driving forces.
Step-by-step explanation: