A Group of Island Birds Have Beaks That Are on Average

Short Answer

A group of island birds have beaks that are on average 20 mm long with a standard deviation of 1 mm. Beak length is a genetically based trait with a heritability of 0.5. Only small seeds are available for these birds to consume, and some of the large-beaked birds are unable to reproduce. The group of birds that successfully reproduces has an average beak size of 16 mm. Based on this information, predict how much the beak size is expected to change in the next generation.