Final answer:
The evolution of beak size on Daphne Major requires that beak size be genetically inheritable and that food sources (i.e., seed characteristics) change over time, not that individuals physically change their beak sizes during their lifetimes. Options A and B are correct, reflecting natural selection based on environmental pressures.
Step-by-step explanation:
The question pertains to the necessary conditions for the evolution of beak size on Daphne Major, home to a population of finches studied by Peter and Rosemary Grant. Of the provided options, number 4) A and B are correct, explains the situation on Daphne Major accurately. First, beak size must be genetically inheritable, controlled by the additive effects of alleles, meaning that genetic variation contributes to the trait of beak size in these finches. Secondly, the variation in the characteristics of the average seed from year to year must exert different selective pressures on the finches' beak sizes. It is not necessary that individuals with smaller beaks grow larger beaks during drought years, as natural selection operates on genetic variation in a population rather than causing direct physical changes in individual organism's traits.
During the drought on Daphne Major, finches with larger beaks were more successful at accessing the limited food resources, primarily bigger and harder seeds, leading to increased survival and reproductive chances as opposed to finches with smaller beaks who struggled to crack these seeds. Consequently, the average beak size within the finch population increased, reflecting natural selection at work.
Over time, this selection process can result in a population with larger average beak size if environmental conditions select against smaller-beaked individuals. This demonstrates a classic example of natural selection driving evolution in a population.