Final answer:
Evidence suggests that nature, not nurture, results in bigger bird or beak size. The study on Galápagos finches by Peter and Rosemary Grant demonstrated that during a drought period, birds with larger beaks were better able to survive and reproduce, leading to subsequent generations with a higher percentage of birds with large, broad beaks.
Step-by-step explanation:
The evidence suggests that it is nature, not nurture, that results in a bigger bird or beak, not just that big birds are raised by big birds. This can be observed in the case of Galápagos finches. Peter and Rosemary Grant's study on the finches showed that during a drought period, the number of small, soft seeds declined more than the number of large, hard seeds. As a result, the birds with larger beaks were better able to survive and reproduce, leading to subsequent generations with a higher percentage of birds with large, broad beaks.