Following article: Stem cells are how we all begin: undifferentiated cells that go on to develop into any of the more than 200 types of cell the adult human body holds. Few quarrel with predictions of the awesome potential that stem cell research holds. One day, scientists say, stem cells may be used to replace or repair damaged cells, and have the potential to drastically change the treatment of conditions like cancer, Alzheimer''s and Parkinson''s disease and even paralysis. But the divisions over how to conduct that research have been deep and bitter. Most research has been conducted on embryonic stem cell lines -- cultures of cells derived from four- or five-day-old embryos, or fertilized cells. Opponents of embryonic stem cell research, which often uses embryos discarded by fertility clinics, want it to be severely restricted or banned outright as inhumane. In August 2001, President Bush limited the use of federal funds to research involving cell lines that already existed, a restriction that many researchers called excessively limiting. As Congress considered legislation to allow broader use of embryonic stem cells, members were swamped with calls from people suffering from diseases for which stem cells research might be the only hope, and from equally vehement opponents. In 2006, the Republican-controlled Congress passed a bill to expand research. In response, Mr. Bush issued the first veto of his presidency. In 2007, Congress, now in Democratic hands, passed a similar bill by a larger margin, but still not by enough to override the veto that Mr. Bush announced on June 20. Barack Obama and Democratic Congressional leaders have made expanding embryonic stem cell research a top priority as they assume full control of the government this year. -- Anahad O''Connor; updated Jan. 12, 2009