Final answer:
The evolution of beak size in Galápagos finches, studied by Peter and Rosemary Grant, demonstrates natural selection, where beak size variations influenced by environmental factors like drought led to changes in the finches' gene pool and demonstrated evolution through survival and reproduction.
Step-by-step explanation:
The study of beak sizes in Galápagos finches is a classic example of natural selection in action. Scientists Peter and Rosemary Grant conducted extensive research on these finches, finding that variations in beak size, which are inherited traits, affected the birds' survival and reproduction. A significant drought in 1977 made small seeds scarce, giving an advantage to finches with larger beaks capable of consuming larger, hard seeds. As these large-beaked birds survived the drought conditions and reproduced, the average beak size within the finch population increased over the following two years, demonstrating the mechanism of evolution by natural selection proposed by Darwin.
Initially, variations in beak size allowed for different feeding efficiencies among the finches. Those with wider and deeper beaks were more efficient in cracking large, hard seeds, while finches with smaller beaks were better suited for smaller, soft seeds. This form of selection, influenced by environmental changes such as drought and the availability of food sources, leads to a shift in the gene pool favoring the traits that enhance survival and reproductive success. The Grants' research provides insight into how such environmental pressures can drive the evolution of certain traits within a population, a concept central to understanding biological diversity.