Clones are created through somatic cell nuclear transfer, an approach to cloning in which the nucleus of an egg cell is replaced with the nucleus of a somatic, or non-reproductive, cell from a person to be cloned. Under ideal conditions, the two fuse together seamlessly, and the egg is activated by a jolt of electricity, then deposited into a womb and allowed to grow and differentiate. If the fertilized egg develops into a fetus and makes it to term, the result is an individual with around 99.7% genetic similarity to the somatic cell donor — a clone. This value is not 100% because there is important DNA in the cell that exists outside the nucleus, which is left behind during the somatic cell nuclear transfer.
Despite beliefs that clones are exact copies of each other, human clones would have less genetic similarity to their clone than they would to an identical twin. Brain patterns coding for details of personality, memories, skills, and the like would not be transferred from the cell donors.
Many claims of successful human cloning have surfaced in the past, only for them to be revealed as hoaxes. A human embryo has been successfully cloned by at least one group — Advanced Cell Technology, an American company that reached this milestone in 2001. However, the embryo only divided a few times and never grew into a true fetus or infant. Certain countries, like Australia, have already passed legislation banning the use of human cloning for any purpose.
A challenge to cloning is that the current process is all manual — a human operator must use a tiny needle to suck the nucleus out of a somatic cell and inject it into an egg cell. The trial-and-error nature of somatic cell nuclear transfer results in a large failure rate for cloning — only 1% to 5% of attempts are successful. There is also a large incentive for scientists to lie about progress in producing clones. For example, in 2004, Korean scientist Hwang Woo-Suk claimed to have successfully created 30 week-old cloned embryos and harvested their stem cells. In 2006, it was determined that his claims were fabricated.