In many tissues, stem cells serve as a sort of internal repair system. They divide essentially without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell that has a more specialized function like a brain cell, red blood cell, or a muscle cell.

In 1998, there were stem cell news about a method discovered by scientists to derive stem cells from human embryos and grow the cells in the laboratory. The embryos used in the studies were created for reproductive purposes through in vitro fertilization procedures. By 2006, researchers have made another breakthrough by identifying conditions that would allow some specialized adult cells to be reprogrammed genetically to take on a stem cell-like state.