Ten years ago, Scottish scientists proved an animal could be cloned — and raised a burning question: Would a human be next?
Before Dolly the cloned sheep, who was euthanized at age 6 due to a lung infection, scientists had been trying for decades to make a clone, or genetic copy, of an animal. To make a clone, a nucleus is removed from an egg and replaced with the nucleus of a cell from the animal to be cloned. The egg is then coaxed to begin dividing. After a few divisions, the cloned embryo can either be transferred to a uterus, or used to derive embryonic stem cells.
Ethical and technical roadblocks to cloning a human embryo remain substantial. At the same time, scientists have made significant advances in cloning animals. Here, a look at cloning developments since Dolly's birth:
Q: In the decade since Dolly was revealed to the world, what practical advances in cloning have been made?
Although cloning still is not an efficient process, scientists have become more efficient at making cloned animals. It still requires dozens, if not hundreds, of fresh eggs to make a cloned embryo, and then only a small fraction of the cloned embryos will produce a live birth after being transferred to an animal's womb.
But the process is efficient enough to make it possible to clone prized barnyard animals for breeding stock, and it may be possible to insert genes into these animals that will give them desirable traits. For example, scientists have inserted a gene into pigs that causes them to produce a kind of fat that is healthier for the human diet. That gene is also passed onto to the clone's offspring, which means whole herds of an animal containing a desirable trait could be created.
Q: Why no announcement of a human clone?
No reputable scientist is attempting to clone a live human being. That said, several teams around the world are trying to make cloned human embryos with the intention of deriving embryonic stem cells. No one has succeeded yet. A South Koren lab's claim to have done that turned out to be fraudulent.
Some species are harder to clone than others. Primates, including humans, have proven especially difficult. At least part of the problem is the scarcity of eggs needed to initiate the cloning process.
Q: Does cloning have the potential to improve our lives?
Cloning animals is an important research tool, because it provides a way of creating animals with desirable traits. This is significant for agriculturally important livestock.
As far as human cloning is concerned, scientists see two primary reasons to make embryonic stem cells from cloned embryos. One, stem cells made from an individual will not be rejected if they are transferred back to that individual in some future therapy. Two, it would be possible to make stem-cell lines from people with specific diseases, thus creating a new way of studying those diseases in cells grown in the laboratory.
Q: Are the ethical issues still the same?
There's still no question that most people consider attempting to clone a human being unethical — at the very least because the cloning process seems to create animals with health problems.
For people opposed to destroying human embryos for any reason, cloned embryos present an ethical dilemma: Since a cloned embryo is a potential human life, it's wrong to destroy it. But those opposed also believe it's wrong to make a cloned human being, so the embryo shouldn't be implanted in a woman, either.
Q: What steps have been taken to prevent the creation of human clones?
In the United States, no steps have been taken to prevent the cloning of a human being. All attempts to legislate on this issue have bogged down, because opponents of cloning want to ban all cloning, whereas scientists say creating embryos and stem cells would be valuable for research. Most other countries in the world do have laws banning so-called reproductive cloning; some also ban all forms of cloning as well.
Q: Has cloning had any impact yet on the average person's life?
No. There are livestock husbandry companies that are hoping to make money by cloning prized animals. Companies offering to clone prized pets have gone out of business.
The FDA has declared meat from cloned animals and their offspring safe to eat, but the agency has asked that businesses not yet put these products on the market. Nor is it yet economically feasible to sell cloned meat; clones are still very expensive to make.