Final answer:
Galapagos finches with larger beaks eat large seeds. Environmental factors like droughts can influence natural selection, affecting beak size in finch populations over time, as demonstrated by the Grants' studies on the Galapagos Islands.
Step-by-step explanation:
Galapagos finches with powerful thick beaks typically eat large seeds. In the Galapagos Islands, the Grants observed that finches with larger beaks had a survival advantage during a drought because they could eat larger seeds, which were more available than smaller ones. As smaller-beaked finches died off, the average beak size in the population increased. This is a classic example of evolution by natural selection, where environmental pressures led to a change in a physical trait across generations. In particular, the medium ground finch of Daphne Major island demonstrated the direct effect of seed availability on beak size. Conversely, during times of plenty, when small seeds were abundant, finches with smaller beaks had a survival advantage. The variation in beak sizes within finch populations on the Galapagos, documented through continuous studies since 1976, showcases the dynamic process of natural selection. Finches exhibit a range of beak sizes adapted for different food sources; however, those with thicker, larger beaks are equipped to crack open and consume the larger, harder seeds.