Our understanding of the human brain is heavily indebted to the study of animal brains. Although the use of animals in biological research raises moral questions about animal rights, there is no question that much of our knowledge about the human brain derives from research on animal brains. Legally and ethically, we can perform much more invasive procedures on animal brains than we can on living human brains. Additionally, comparison of the brains of many different kinds of animals gives us critical insight into brain evolution.