THE SCIENCE:
Researchers have successfully isolated stem cells from five-day-old human embryos that were created during in-vitro fertilization and that would otherwise have been destroyed. Unlike adult stem cells, embryonic stem cells can develop into any one of more than 200 tissues in the body, from insulin-producing cells that may one day treat diabetes to heart cells that may repair cardiac muscle.
THE ETHICS:
Since the embryos were scheduled to be tossed, many view this as the best compromise; others believe generating tissue from human embryos is never acceptable.