THIS year’s Nobel prize for medicine went to Sir John Gurdon and
Shinya Yamanaka (both pictured above) for a crucial discovery in
stem-cell science: how to make what are known as pluripotent
stem cells from ordinary body cells. What the citation did not
say was that this work also allows clones to be made from adult
animals, potentially including people.  A stem cell is one that
can differentiate into daughter cells specialised for particular
functions, and all the cells in a body are thus derived from
stem cells. That includes the stem cells themselves, which
derive from “ur” stem cells found in embryos. These embryonic
stem cells are the pluripotent ones, meaning they can turn into
many (sometimes all) other sorts of cell.  Pluripotent embryonic
stem cells are of great value to researchers but, if the embryos
they come from are human, their use is controversial. This
controversy, indeed, was what had originally stimulated Dr
Yamanaka to start his investigations, in the hope that embryonic
cells might no lon