May the Biggest Beak Win
In a population of finches, some have little beaks that can only crack open small, soft seeds; others have big beaks that can open big seeds; and still others fall somewhere in between. During times of food scarcity (such as a drought), the big-beaked birds are more likely to survive and reproduce because they have a greater variety of seeds to choose from. Looking at the finch population during this period, you will see more birds being born with bigger beaks. It’s natural selection right before your eyes (Grant, 1991).