Human cloning has long captivated public imagination, often appearing in science fiction. This raises questions about its scientific feasibility and the complex considerations surrounding such a possibility. Understanding the science and societal discussions requires looking beyond speculative portrayals to biological processes and ethical frameworks.
How Cloning Works: The Science
The primary scientific method for cloning mammals is Somatic Cell Nuclear Transfer (SCNT). This process begins with obtaining a somatic cell, which is any cell from the body other than a sperm or egg cell. The nucleus, containing the complete genetic material of the donor organism, is removed from this somatic cell. Simultaneously, an unfertilized egg cell from a different donor has its nucleus removed, rendering it “enucleated.”
The next step involves transferring the somatic cell nucleus into the enucleated egg cell. The reconstructed egg is then stimulated, often with an electrical pulse or chemical treatment, to initiate cell division and development. If successful, this stimulation causes the cell to behave like a newly fertilized embryo, developing into a blastocyst, an early-stage embryo. This blastocyst, genetically identical to the somatic cell donor, can then be used for various purposes.
Cloning in the Animal Kingdom
The scientific feasibility of cloning from adult cells was demonstrated with Dolly the sheep, born in 1996. Researchers at the Roslin Institute in Scotland used a mammary gland cell from an adult ewe for the SCNT process, creating the first mammal cloned from an adult somatic cell. Dolly’s birth was a milestone, proving that genetic material from a specialized adult cell could be reprogrammed to generate a new organism.
Since Dolly, numerous other mammals have been successfully cloned using SCNT, including mice, cats, dogs, pigs, cows, horses, and monkeys. The first dog, Snuppy, was cloned in 2005, and two crab-eating macaques, Zhong Zhong and Hua Hua, were cloned in 2018, marking the first successful primate cloning. Despite these successes, the efficiency of animal cloning remains relatively low, with success rates typically ranging from 1 to 2 percent in mice and 5 to 20 percent in cattle. Many attempts result in developmental abnormalities or failures during pregnancy, highlighting the technical challenges in this field.
Why Not Humans? Ethical and Legal Considerations
The scientific capability to clone animals does not automatically translate to human application, primarily due to ethical and legal barriers. An ethical concern revolves around the high failure rates observed in animal cloning, which often lead to miscarriages, stillbirths, and severe developmental abnormalities. Applying a process with such a low success rate and high risk of harm to human beings is widely considered unacceptable, posing physical risks to any potential cloned individual and the surrogate mother.
Concerns also extend to the psychological and social well-being of a cloned human. Questions about individuality, identity, and the potential for a cloned person to feel like a mere copy rather than a unique individual are central to the ethical debate. There are worries about potential exploitation, such as creating individuals for specific purposes or engaging in practices reminiscent of eugenics, which violates human dignity and equality. The global community has largely prohibited human reproductive cloning, with many countries enacting specific laws. Over 46 countries have banned human cloning, and international bodies like the United Nations have issued declarations against it.
The Different Faces of Human Cloning
Public discussions about human cloning often conflate two distinct applications: reproductive cloning and therapeutic cloning. Reproductive cloning aims to create a genetically identical copy of an organism, with the intent of developing it into a full-term individual. This type of cloning raises the most ethical and legal objections, as it involves creating a human being based on another’s genetic blueprint.
Therapeutic cloning, also known as research cloning, shares the initial SCNT steps but has a different objective. Cloned embryos are created not for implantation into a womb, but to generate patient-specific embryonic stem cells for medical research and potential treatments. These stem cells, genetically identical to the patient, could be used to develop tissues or organs for transplantation without immune rejection, offering avenues for treating diseases like Parkinson’s, Alzheimer’s, or diabetes. The ethical debate centers on creating and destroying human embryos to harvest stem cells, a practice viewed as morally objectionable by some who believe an embryo has potential for personhood. Despite these debates, some countries, such as the United Kingdom and parts of Australia and Asia, permit therapeutic cloning under strict regulatory frameworks, acknowledging its medical benefits while prohibiting reproductive cloning.