Stem cells are unspecialized cells that can reproduce themselves for long periods of time using cell division, but are also capable of differentiating into almost any type of specialized cell. This unique ability makes them ideal for use in regenerative medicine. Adult stem cells are derived from umbilical cord blood and bone marrow. Embryonic stem cells are also used in medical research, but their use is more controversial. Why is there an ethical debate surrounding embryonic stem cell use? Discuss