For National Geographic News
In an awe-inspiring scene from Episode II: Attack of the Clones, a mass-produced legion of identical men appears to march off an assembly line like so many Ford Model T's. The cloned soldiers look, think, and act alike, and their performance in battle proves beyond a doubt that they are hearty and hale members of the human race.
But scientific theory and experience in the lab show that cloningeither people or animalsmay not be as easy as science fiction makes it look. Scientists are still struggling to understand whether it's even feasible to reliably coax molecules of DNA extracted from a single cell to develop into a living genetic replica of an entire organism.
"Cloning is as much an art as it is a science," said Robert Lanza of Advanced Cell Technology in Worcester, Massachusetts.
So while politicians, ethicists, and voters grapple with the vexing questions that surround the morality of cloning, scientists are struggling with a biological rather than an ethical problem: Cloning people might not be safe.
Successand Many Failures
After years of experiments involving frogs, salamanders, and simpler organisms, cloning hit the big time in February 1997. That month, scientists reported the first successful attempt to reproduce a large, adult mammal through cloning. Nicknamed Dolly, the cloned sheep became an instant media darling and a symbol of the scientific promise of cloning.
Since Dolly, cows, pigs, monkeys, an adorable kitten, and even rare and endangered animals have all been produced through cloning. Some of these have survived to be adults and even reproduced.
But other clones have experienced terrible health problems, and many cloned embryos don't even survive to birth. Not everyone realizes that Dolly was the final success story at the end of a string of unsuccessful attempts and spontaneous abortions. Scores of sheep embryos died before they had even developed to a stage at which scientists could insert them into a live female.
A Complex Process
Cloning an animal is a complex process that can go fatally wrong at any stage. The process, also called nuclear transfer, begins when a nucleus is removed from an egg cell. This DNA-containing packet is discarded.
Next, a nucleus with a complete set of DNA is meticulously extracted from a single cell, itself removed painlessly from the skin or body of the living organism that's to be cloned. That nucleus is transferred by a delicate operation into the nucleus-deprived egg.