Final answer:
The increased beak size in finch offspring post-drought on Daphne Major exemplifies natural selection, where finches with larger beaks survived and reproduced, leading to a larger average beak size in the population.
Step-by-step explanation:
The difference in beak size between offspring of finches that survived the drought of Daphne Major and the population average before the drought is an example of natural selection. During the drought, there was a shortage of small seeds, leading to a higher mortality rate among finches with smaller beaks. Those with larger beaks survived more successfully and reproduced, thereby increasing the average beak size in the finch population. This shift in trait frequency due to the environmental pressure is a clear demonstration of natural selection in action, as outlined by the extensive research conducted by Peter and Rosemary Grant on the Galápagos finches.