Stem cells don’t simply transform themselves into other cells (a process called differentiation) to build what the body needs and then, their work done, quietly disappear. They are more than the progenitors of other cells. They also replicate themselves—in an unrefined, undifferentiated state—so that they can stick around to answer the call later when the blood system needs rebuilding. —Joe Sornberger, Dreams and Due Diligence
