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 the long-held ...