THE SCIENCE:
Certain primitive cells found in the brain, blood and elsewhere in the body remain undeveloped enough even in adults that they can grow into a limited number of cell types. (Neurons are pictured above.) These cells might be coaxed to become a wider variety of tissues.
THE ETHICS:
An acceptable avenue of research to most people but the least practical option scientifically because adult stem cells may not prove as versatile as embryonic ones.