This process develops from mutations that occur randomly. For example, animal parents with brown fur may give birth to an offspring that has abnormal black stripes. Animals that have any slight advantage for better survival have a better chance of producing more offspring. Over time, the population may have a greater number of black-striped individuals because they survive better and produce more offspring. 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.