In 2006, Dr. Shinya Yamanaka and his co-workers took genes that were known to inhibit stem cell specialization in order to see how specialized cells could be reverted into their embryonic state. After much trial and error, it was discovered that four genes introduced into fibroblasts, mature cells of the connective tissue, could revert the cells back to embryonic stem cells. These stem cells could then be specialized into different cells. (Citation 10)