Dolly, born in July 1996, was the first mammal cloned from a fully developed adult cell. Hers was the only one of 277 cloned embryos to develop into a healthy lamb.

Cloning creates a genetically identical copy of an individual by reprogramming eggs with genetic material from a donor.

The 1996 birth of a cloned sheep named Dolly thrust cloning into the spotlight. Since then, further achievements in cloning animals—sheep, cows, mice, pigs and goats—have spurred debates on how we should apply this technology. Cloning endangered species could boost populations but may not save species from extinction. Cloned livestock could increase production but may reduce herd diversity. Soon we may even clone family pets, but Rover's clone may not fetch like Rover.

Are Humans Next?

The biggest question is whether we will clone ourselves. Today human cloning is technically possible, but many experts say it's unethical, and public opinion polls show that most people oppose it. Some governments have banned human cloning, while others have left the door open. As society weighs the risks and benefits, a few scientists are forging ahead and expect to succeed—soon. Stay tuned.