Comparative anatomy
The great era of comparative anatomy was from about 1800 to about 1950. It was used by those who did not believe in evolution, such as Georges Cuvier, and by those who did, such as Thomas Henry Huxley. Charles Darwin himself used comparative anatomy as the main tool in his work on barnacles. Nowadays, the main method used to find out relationships is molecular evolution, which uses DNA sequence analysis. However, for many research purposes, zoologists still dissect animals. To get a degree in biology, you need to know about the structure of animals (and plants).