|Photo: E.D. Laywell, UT Memphis|
Multipotent clones of cells derived from the adult human brain
A paradigm shift occurs as exceptions, often startling ones, accumulate to the point that scientists need to sit back and reevaluate prevailing theories. In outlining the criteria for a paradigm shift in 1962, Thomas Kuhn wrote, "Such changes, together with the controversies that almost always accompany them, are the defining characteristics of scientific revolutions."1
Stem cell research is upsetting...