Final answer:
True, the Darwin units indicating evolutionary change in Galapagos finches' beak sizes during the 1970s and 1980s drought and flood years are high, demonstrating rapid natural selection and microevolution.
Step-by-step explanation:
True, the number of Darwin units that describe the rate of change in Galapagos finches during the drought and flood years of the 1970s and 1980s is high in evolutionary terms. This rapid rate of change was observed by Peter and Rosemary Grant, who provided conclusive evidence of natural selection and microevolution in the beak sizes of Galapagos finches—specifically the medium ground finch on Daphne Major. For instance, during the drought of 1977, the small-beaked finches could not compete with large-beaked finches for the limited large, hard seeds that were available. As a result, many of the small-beaked birds died, leading to an increase in the average beak size among the finches. Conversely, during the El Niño years with more rainfall, an abundance of small, soft seeds favored the survival and reproduction of small-beaked birds, eventually resulting in a decrease in average beak size. These fluctuations were dramatic examples of evolution via natural selection over a short period, hence the reference to a high number of Darwin units.