Zoology 10th Edition by Stephen Miller,John Harley

Exercise 15

The evidence described by Charles Lyell convinced Darwin that the earth was millions of years old, a time period long enough to account for changes in living organisms. South American fossils and observations of tortoises and finches on the Galápagos Islands convinced Darwin that change in organisms over time does occur. These observations, and others, were the basis for his description of the mechanism of evolutionary change.
How does the example of Galápagos finches illustrate the concept of adaptive radiation?