Stem cells are totipotent cells that can differentiate into any body cell type. Scientists first researched mouse bone marrow stem cells in 1963 and have since tried using bone marrow stem cells for transplants. Stem cells can potentially be used to treat nervous system diseases, injuries, genetic disorders, and more because they can become any cell needed. However, embryonic stem cell research requires destroying embryos and carries cancer risks, causing ethical debates. Now, scientists can turn adult skin cells into stem cells to avoid rejection and new methods avoid cancer risks.