It’s the study of similarities and differences in the anatomy of organisms. It’s linked with the evolution of species.
There are three main concepts:
– Homologous structures: a similar structure in different animals because of common descent. For example a bat has a similar structure that a bird.
– Analogous structures: structures similar in different organisms because they evolved in a similar environment. An example is the streamlined torpedo body shape of porpoises and sharks. So even though they evolved from different ancestors, porpoises and sharks developed analogous structures as a result of their evolution in the same aquatic environment.
– Vestigial structures: are in a degenerate, atrophied, or rudimentary condition. An example of this: in whales, can find small vestigial leg bones deeply buried within the back of the body. These are remnants of their land-living ancestors’ legs.