Harvard-affiliated researchers said Tuesday they have begun efforts to create stem cells by cloning human embryos, joining the race among a small group of scientists in this controversial pursuit. The work at Children's Hospital Boston, the main pediatric teaching hospital of Harvard Medical School, is aimed at eventually creating stem cells for treating blood diseases like sickle-cell anemia, leukemia and other blood disorders. Dr. George Daley, a leading expert in blood diseases, is overseeing the work at the hospital. Daley, an executive committee member of the Harvard Stem Cell Institute, said he had begun experiments but declined to describe the...