How old was Dolly the sheep when she died

It was a glorious day in the hills above Edinburgh, Scotland, when old friends and scientific colleagues Ian Wilmut and Alan Trounson set off on a hike two decades ago. High over the city, Wilmut confided that he had a secret to share. As part of a larger study, he and several co-workers had successfully birthed a lamb in the lab—not from egg and sperm but from DNA taken from an adult sheep’s mammary gland. They had cloned a mammal. “Crikey, I was stunned,” says Trounson, who is now—as then—a stem cell biologist at Monash University in Melbourne, Australia. He remembers sitting down hard on a nearby stone. It was a warm day but Trounson felt a chill pass over him as he realized the implications. “It changed everything.”

Cloning a mammal defied the scientific dogma of its time. The success led to dire and fantastic predictions: Humans would be cloned. Diseases would be prevented. Lost children rebirthed. Today, two decades after Dolly’s birth on July 5, 1996, the impact of cloning on basic science has surpassed expectations whereas the reality of what is technically called nuclear transfer—the form of cloning used with Dolly—has largely faded from public consciousness.

In 2016 cloning a person remains unfeasible, with no scientific benefit and an unacceptable level of risk, several scientists say. Most know of no one even considering the feat. And the cloning of animals remains limited—although it is likely growing. Some agricultural cloning is used in the U.S. and China to capitalize on the genes of a few extraordinary specimens, scientists say, but the European Parliament voted last year to ban cloning animals for food. One scientist in South Korea charges $100,000 to clone pets, although the level of demand for the service is unclear.

Cloning’s biggest impact, several researchers say, has been in the stem cell advances it has sparked. Stem cell biologist Shinya Yamanaka said via e-mail that Dolly’s cloning motivated him to begin developing stem cells derived from adult cells—an accomplishment that won him a Nobel Prize in 2012. “Dolly the Sheep told me that nuclear reprogramming is possible even in mammalian cells and encouraged me to start my own project, wrote Yamanaka, who splits his time between the University of California, San Francisco, and the Center for iPS Cell Research and Application (CiRA) at Kyoto University in Japan, which he directs. He used adult cells—first in mice, although the technique is now feasible in human cells—to make stem cells that can form a wide range of other cells, essentially turning their cellular clocks back to infancy so they could mature into different adults. Because they are artificially created and can have a variety of futures, they are called induced pluripotent stem (or iPS) cells. The rise of these iPS cells has reduced the need for embryonic stem cells—which have long caused ethical concerns for some—and iPS cells now form the basis for most of today’s stem cell research.

Dolly’s birth was transformative because it proved that the nucleus of the adult cell had all the DNA necessary to give rise to another animal, says stem cell biologist Robin Lovell-Badge, head of the Division of Stem Cell Biology and Developmental Genetics at the Francis Crick Institute in London. Previous researchers had derived adult frogs from embryonic frog cells or embryonic frog cells from adults—at which point their development stalled. “Dolly was the first example of taking an adult cell and getting an adult,” Lovell-Badge says. “That meant you could reprogram an adult cell nucleus back to an embryonic stage.”

Dolly died on February 14, 2003, at age six from a lung infection common among animals who are not given access to the outdoors. It probably had nothing to do with her being a cloned animal, says Wilmut, now an emeritus professor at the The Roslin Institute at the University of Edinburgh where he did his initial work.

The sheep, made from breast cells, was famously named after Dolly Parton, the American singer known for her large chest as well as her voice. “It wasn’t meant to be disrespectful to the lady in question or to women in general,” Wilmut said recently, of the name suggested by a stockman. Rather, it helped humanize a research project that might otherwise have seemed detached from everyday life. “Science and its presentation can sometimes look terribly serious,” he said. “I think it was good for us—it made us look human.”

Wilmut admits Dolly’s birth was a lucky accident. He and his colleagues were trying to make clones from fetal cells and used adult ones as experimental controls—not expecting that they would actually generate an embryo of their own. “We didn’t set out to clone adult cells. We set out to work with—ideally—embryonic stem cells or things like that,” Wilmut says. “Being successful with adult cells was a very considerable, unexpected bonus.”

The initial aim of the research was to use an animal’s milk production system as a factory of sorts, manufacturing proteins to treat human diseases. But interest in that idea has declined with the rise of inexpensive synthetic chemicals.

Wilmut says he thinks it would be possible to clone a human—but highly unadvisable. The cloning technique used to create Dolly has been shown not to work in primates. He believes it could be possible using other techniques but said he is vehemently opposed to the idea of cloning a person. “Just because it may now work in the sense of producing offspring doesn’t mean to say we should do it,” he says. “The likelihood is you would get pregnancy losses, abnormal births.” For example, one of the lambs his lab cloned soon after Dolly developed lung problems that caused it to hyperventilate and regularly pass out. “It was distressing enough to see that in an animal,” he says. “I wouldn’t want to be the person who looked a cloned child in the face and said ‘very sorry.’” With recent advances in gene-editing technology, the need for cloning to correct genetic errors will decline even further, he notes. “There’s even less reason for doing it now than before.”.

Trounson says he believes there is a large market for cloned livestock embryos. “It’s pretty busy out there, kind of surprisingly and below the surface,” he says. “The benefits genomically for production excellence and driving up production parameters is very good,” adds Trounson, who recently stepped down after six years as president of the California Institute for Regenerative Medicine, a state agency that provides loans and grants for stem cell research. “That’s probably the driver that has kept companies doing it in the U.S.”

The U.S. government decided in 2008 that there were no discernable differences between cloned and noncloned cows, goats and pigs, so it allowed the process in those animals, although mainly for breeding rather than meat production. In China a company called Boyalife Group has plans to produce at least 100,0000 cloned beef cattle—a fraction of the total number of animals slaughtered each year in that country, a company spokesperson wrote via e-mail. “We might be at the best time to advance this technology into applications from both a technology perspective and from a market perspective [in China].”

Theoretically, cloning could also be used to bring back endangered species. There has been talk of using it to restore woolly mammoths, giant pandas and even Neandertals—ideas Lovell-Badge dismisses as “fairly silly.” Trounson says he still has a stash of skin samples from critically endangered northern hairy-nosed wombats stored in liquid nitrogen, in case someone ever wants to attempt to restore the species’s numbers. Clones, however, are created by taking an adult cell and fusing it to a recipient egg cell. Making a clone requires an intact nucleus, which would not be available for most extinct species.

Several researchers are now using cloning techniques to produce embryonic stem cells, thereby avoiding the need to collect new embryos. So-called somatic cell nuclear transfer may help researchers better understand early human embryogenesis and stem cell biology, according to Paul Knoepfler, a biologist at the University of California, Davis, who is not directly involved in the work. Knoepfler wrote via e-mail that he does not “see any imminent therapeutic benefit [to that work], but that could change in the future.”

The idea of cloning a deceased loved one—human or pet—has fallen out of favor in part because of the recognition that environment affects behavior. The genetics might be the same but would a clone still be the same lovable individual? “You’re never going to get Tibble back, or whatever,” Lovell-Badge says, noting that he thinks the idea of cloning a pet is “stupid.” He adds, “The only possible use that I can sort of vaguely think of is if you have a particular valuable dog,” with skills like super-sniffing that scientists would want to determine was inborn or behavioral.

Lovell-Badge is even more dismissive of the idea of cloning a person. “We’d have to know an awful lot more about reprogramming and how to make it 100 percent efficient,” he says. “I have never thought of a good enough reason for a human being.”

Making Dolly

Dolly and her surrogate mother

Dolly was part of a series of experiments at The Roslin Institute that were trying to develop a better method for producing genetically modified livestock. If successful, this would mean fewer animals would need to be used in future experiments. Scientists at Roslin also wanted to learn more about how cells change during development and whether a specialised cell, such as a skin or brain cell, could be used to make a whole new animal.

These experiments were carried out at The Roslin Institute by a team led by Professor Sir Ian Wilmut. Because of the nature of the research, the team was made up of many different people, including scientists, embryologists, surgeons, vets and farm staff.

Dolly was cloned from a cell taken from the mammary gland of a six-year-old Finn Dorset sheep and an egg cell taken from a Scottish Blackface sheep. She was born to her Scottish Blackface surrogate mother on 5th July 1996. Dolly’s white face was one of the first signs that she was a clone because if she was genetically related to her surrogate mother, she would have had a black face.

Because Dolly’s DNA came from a mammary gland cell, she was named after the country singer Dolly Parton.

Learn more about cloning with our cloning FAQs.

Why was Dolly so important?

Dolly was important because she was the first mammal to be cloned from an adult cell. Her birth proved that specialised cells could be used to create an exact copy of the animal they came from. This knowledge changed what scientists thought was possible and opened up a lot of possibilities in biology and medicine, including the development of personalised stem cells known as iPS cells.

However, Dolly was not the first ever cloned mammal. That honour belongs to another sheep which was cloned from an embryo cell and born in 1984 in Cambridge, UK. Two other sheep, Megan and Morag, had also been cloned from embryonic cells grown in the lab at The Roslin Institute in 1995 and six other sheep, cloned from embryonic and foetal cells, were born at Roslin at the same time as Dolly. What made Dolly so special was that she had been made from an adult cell, which no-one at the time thought was possible.

Dolly’s life

Dolly was announced to the world on 22nd February 1997 to a frenzy of media attention. The Roslin team chose to make the announcement at this time to coincide with the publication of the scientific paper which describes the experiments that produced her. Dolly captured the public’s imagination – no small feat for a sheep – and sparked a public debate about the possible benefits and dangers of cloning.

Dolly meets the world’s media. Image copyright: Murdo Macleod

In the week following the announcement, The Roslin Institute received 3,000 phone calls from around the world.

When Dolly was one year old, analysis of her DNA showed that her telomeres were shorter than would be expected for a normal sheep of the same age. Telomeres are ‘caps’ on the ends of DNA molecules that protect the DNA from damage. As an animal or person ages, their telomeres become progressively shorter, exposing the DNA to more damage.

It’s thought that Dolly had shorter telomeres were because her DNA came from an adult sheep and the telomeres had not been fully renewed during her development. This could have meant that Dolly was ‘older’ than her actual age. However, extensive health screens on Dolly at the time did not find any conditions which could be directly related to premature or accelerated ageing.

Dolly and Bonnie

Dolly spent her life at The Roslin Institute and, apart from the occasional media appearance, led a normal life with the other sheep at the Institute. Over the years Dolly had a total of six lambs with a Welsh Mountain ram called David. Their first lamb, Bonnie, was born in April 1998, twins Sally and Rosie were born the following year and triplets Lucy, Darcy and Cotton the year after.

After Dolly gave birth to her last lambs in September 2000, it was discovered that she had become infected by a virus called Jaagsiekte sheep retrovirus (JSRV), which causes lung cancer in sheep. Other sheep at The Roslin Institute had also been infected with JSRV in the same outbreak.

In 2001, Dolly was diagnosed with arthritis after farm staff noticed her walking stiffly. This was successfully treated with anti-inflammatory medication, although the cause of the arthritis was never discovered.

Dolly continued to have a normal quality of life until February 2003, when she developed a cough. A CT scan showed tumours growing in her lungs and the decision was made to euthanise Dolly rather than risk her suffering. Dolly was put to sleep on 14th February 2003, at the age of six.

Where is Dolly now?

After her death The Roslin Institute donated Dolly’s body to the National Museum of Scotland in Edinburgh, where she has become one of the museum’s most popular exhibits. Dolly is back on display in the museum after an extensive gallery refurbishment, alongside an interactive exhibit on the ethics of creating transgenic animals featuring current research from The Roslin Institute.

National Museums Scotland blog post – ‘Goodbye Dolly’