Reproductive Cloning
The use of nuclear-transfer techniques to produce a living organism genetically very similar to an existing one. Done in animals, not in humans, and broadly prohibited.
When people use the word “cloning” in everyday conversation, they almost always mean reproductive cloning: the idea of producing a living being whose DNA closely matches another. It is the version that captures the imagination, and it is also the version about which the most common assumptions are wrong.
What reproductive cloning is
Reproductive cloning, in mammals, is the use of somatic cell nuclear transfer (SCNT) to produce an embryo whose nuclear DNA matches a donor body cell, and then to attempt a pregnancy from that embryo. If the pregnancy succeeds, the resulting animal is described as a clone of the donor.
Dolly the sheep, announced in 1996, was the first mammal produced this way from an adult somatic cell. Since then, scientists have reproductively cloned many species, including mice, cattle, pigs, goats, cats, dogs, and macaque monkeys.
What reproductive cloning has not done
It has not produced a verified human clone. Claims to the contrary, including from groups promising imminent human clones, have not been supported by independent scientific evidence. The leading peer-reviewed literature, national academies, and international health bodies treat reproductive human cloning as an unaccomplished and broadly prohibited possibility.
Why it is considered unsafe
Even in animals, reproductive cloning has been technically difficult and biologically costly. Across published studies, the following patterns recur:
- Very low success rates. Many SCNT pregnancies fail in early development.
- Developmental abnormalities. Surviving cloned animals have shown rates of birth defects and physiological problems above those of conventionally conceived animals.
- Epigenetic instability. The chemical marks that tell genes when to switch on and off are difficult to fully reset, which appears to be linked to some of the abnormalities seen in cloned animals.
Extending those risks from animals to a human pregnancy is generally considered unacceptable to medical-ethics frameworks. That safety concern alone, before any further ethical objection, is enough to push reproductive human cloning outside the scope of acceptable practice in the peer-reviewed scientific literature.
Why the ethical concerns go beyond safety
If the safety problems were solved tomorrow, reproductive cloning would still face serious ethical objections. Among the most consistently cited:
- Identity. A reproductive clone would grow up alongside the cultural expectation of being a copy of someone else. That is a heavy burden to place on a person.
- Consent. A future person cannot consent to the conditions of their own creation. Reproductive cloning makes a deliberate decision about a person before they exist.
- Dignity. Major international declarations frame reproductive cloning as incompatible with human dignity. That framing has shaped national laws around the world.
- Family and legal status. Cloning blurs ordinary relationships in ways that current family and inheritance law has not resolved.
- Inequality and pressure. Powerful reproductive technologies historically concentrate among the wealthy and can be used in ways that put pressure on people in less powerful positions.
Editorial note
This site does not advocate for the legalisation of human reproductive cloning. It also does not advocate against responsible research on the underlying biology. Our role is to explain, not to campaign.
What about “identical”?
The intuitive idea of reproductive cloning is that it produces a perfect duplicate. Biology does not behave that way. Even in cloned animals:
- Mitochondrial DNA comes from the donor egg, not the nuclear-donor body cell.
- Cells acquire epigenetic differences during development.
- Environment shapes growth, behaviour, and physiology in major ways.
Cloned animals are genetically very similar to their donors, but the romantic notion of two indistinguishable individuals is misleading. The clone is its own creature.
Key takeaway
Reproductive cloning has been done in many animals but not in humans. It is broadly prohibited, treated as unsafe, and ethically contested for reasons that go well beyond safety alone.