Animal models. The ways the bodies of many different animals work have very great overlaps and things in common. Thus, when scientists study one animal species they can often apply that knowledge to other species as well. This is the major principle that underlies the use of animals to advance our understanding of the way the human body works — animals are used to model body processes in people. Our knowledge of the workings of virtually every system of the human body has been developed in this way.

This modelling principle also underlies the use of knowledge obtained in one animal species to help another animal species (e.g., knowledge about digestion of food in the gut of sheep helps us to better manage cattle). Even when major differences are present between the ways the bodies of different animal species work, those differences, once explained, can greatly improve our understanding of how the bodies of each of the compared species work.