Assertion: Darwin's finches are a classical example of natural selection. Reason : Darwin explained that the difference in size and shape of the beaks of the species was a result of the adaptation of the species to different food habits.

Step-by-step solution

Darwin's finches represent an excellent example of adaptive radiation. Darwin's finches showed wide variations in beak shape and size from island to island. Darwin deduced that these variations made the finches better adapted to take advantage of the food in their particular local environment - thin, sharp beaks prevailing where the birds' main food was insects and grubs, and large claw shaped beaks where their diet was buds, fruits and nuts.