Figure 19.17 Heterometry and the Beaks of Finches (A) Bird beaks can be measured in three dimensions (length, width, and depth) for the purpose of comparing different species. (B) Among Galápagos finches, mutations resulting in different patterns of BMP4 and calmodulin (CaM) expression may be responsible for the different species’ beak sizes and shapes, which are suited for exploiting different types of food.