Certain animals display astonishing regenerative abilities. Some invertebrate species, such as hydra, flatworms and tunicates, can restore their entire body from a fragment of it. Among vertebrates, salamanders and fish can efficiently replace amputated appendages and complex organs. Among mammals, mice and rats are the most common animal models to study stem cell differentiation, wound healing and tissue homeostasis. Researchers do not yet understand why the natural regenerative capacity varies between species. Beside animal studies, cell culture approaches are fundamental for stem cell research.