'''Adult stem cell''' research is similar except it does not use destroyed embryos, and instead is based on stem cells that can be taken from adults. These cells are less versatile than those harvested from discarded embryos, but they do not raise the associated [[ethics|ethical]] dilemmas <ref>http://www.isscr.org/science/faq.htm</ref> and so far have been easier to work with in achieving results.
The primary reason for wanting to use embryonic stem cells is that they are capable of producing any type of tissue in the body. Thus, theoretically, embryonic stem cell treatments offer far greater potential than adult cells - while both are capable of repairing some damage, embryonic cells could go so far as to replace entire organs. Conversely though, the greater flexibility of embryonic cells also makes them more difficult to control. A major obstacle to their use in humans is a tendency to form tumors. Much research is being carried out to better understand the cellular processes which cause this.
*President Bush's refusal of federal funding for new embryonic stem cell lines didn't halt major stem-cell advances, any more than the prohibition against life-threatening research on human subjects, such as the infamous Tuskegee Study of Untreated Syphilis in the Negro Male, stopped the advance of medical treatments. [http://www.opinionjournal.com/federation/feature/?id=110010915 Trading Places] - Will the secular left soon attack the religious right for being pro-science? - Joseph Bottum