Double Trouble.

The Clone Wars are about to begin in the Star Wars movies, but they're also heating up not so long ago and not so far away.

The U.S. Congress held a hearing on human cloning last month after a handful of private groups said they planned to start human experiments. Though advocates say the work could aid transplants, fertility, and other research, critics object to the idea of human cloning on moral and ethical grounds (see Opinion).

The U.S. may ban human cloning, fearing results similar to those with animals. Ongoing since 1997, animal cloning is still an imperfect, and deadly, science. About 97 percent of attempts fail, with genetic abnormalities killing clones near birth. Those that do survive can develop unpredictable problems, such as mouse clones that suddenly become obese in adulthood. But experts say, with money and history on the line, it's only a matter of time before a human clone is created.