This is called natural selection. Mutations occur all the time in living organisms. Some mutations turn out to be beneficial so they have a chance of being passed on through successive generations. Mutations that are not beneficial to the individuals generally disappear. Because biological classifications are based on how organisms are related, the study of body structures helps scientists to understand relationships between organisms.
Dolphins are more similar to other mammals than they are to other classifications of animals.
By comparing the skeletal structure of various animals, students can see these similarities. This comparison will also help students better relate anatomical structures to functions.