Final answer:
Darwin's finches illustrate natural selection due to their diverse beak shapes, adapted for various food sources. Environmental changes influence selective pressures that affect survival and reproduction, leading to changes in populations' genetic traits over generations.
Step-by-step explanation:
Darwin's finches provide one of the best examples of natural selection in action. In the Galápagos, these finches exhibit a variety of beak shapes, each adapted to different food sources. The variation in beak shapes among species like the large ground finch, the medium ground finch, the small tree finch, and the green-warbler finch represents a case of adaptive radiation following a pattern of inheritance that facilitates evolution of particular traits.
The work of Peter and Rosemary Grant on Daphne Major provided clear evidence of this evolutionary process. They documented changes in the distribution of beak sizes as a response to environmental pressures. For instance, during a period of drought, finch populations with larger beaks capable of feeding on the remaining large, hard seeds had better survival and reproduction rates. This led to an increase in average beak size within the population. Alternatively, during times when small soft seeds were more abundant and large hard seeds scarce, birds with smaller beaks had a survival advantage, leading to a decrease in average beak size. This showcases how environmental factors can lead to selective pressures that drive changes in a population's genetic makeup over time.