Many species can regrow limbs or even more. A flatworm can grow a replacement head and brain. A Mexican salamander can regenerate everything even its spinal cord. And young humans can grow back a sliver of a fingertip.
Michael Levin thinks that humans someday will be able to regrow limbs. Levin is director of the Center for Regenerative and Developmental Biology at Tufts University. His research specialty is bioelectricity and he has had some amazing results in developmental biology.
The work of his team has so far been with amphibians such as tadpoles. This spring they will start working with mice. If the techniques work on mammals, the research may someday turn into drugs and medical devices that let humans regenerate limbs, eyes, etc.