Every person begins as just one cell — a fertilized egg. That cell rapidly divides, forming a cluster of cells that will eventually become all the types of cells in all the organs needed to create a whole human being. This cluster of embryonic stem cells has the unique ability to differentiate into any kind of cell in the body, such as brain cells or skin cells.
Scientists had long believed that once stem cells turned into a specific type of cell, they were mature and forever locked in that role. But this year’s Nobel Prize winners in physiology or medicine, John B. Gurdon and Shinya Yamanaka, disproved this dogma by discovering that specialized, fully developed cells can be reprogrammed back into undifferentiated states.