Are animals too different from people for animal research to be valid?

Obviously there are differences between animals and people. But under the skin, the biology of humans and other animals, particularly mammals, is remarkably similar. We have the same organs, controlled by the same nerves and hormones, as many other species. Where there are differences, researchers know about them, and such differences can actually help scientific understanding of a particular problem. Many animals suffer quite naturally from the same diseases as humans, and can be used to study those diseases. In other cases, researchers can use an 'animal model' of a disease which is close to the human condition.