Let's look at how evolution might occur. Species A is a bird with a medium beak size that feeds on small- and medium sized seeds. Every generation, a few birds are born with slightly larger beaks. These birds can feed on slightly larger seeds than their medium-beaked relatives. The larger. beaked birds now have an advantage. They have access to a food with fewer competitors. With each generation, more birds that have inherited this larger beak variation will be born into the population.