Animals are appropriate research subjects because they are similar to human beings in many ways. Chimpanzees share 99% of their DNA with humans, and mice are 98% genetically similar to humans. [9] All mammals, including humans, are descended from common ancestors, and all have the same set of organs (heart, kidneys, lungs, etc.) that function in essentially the same way with the help of a bloodstream and central nervous system. [17] Because animals and humans are so biologically similar, they are susceptible to many of the same conditions and illnesses, including heart disease, cancer, and diabetes. [18]