Chinese scientists have cloned two monkeys using a technique that could see hundreds of identical primates and possibly identical humans being created.
Using the process that created Dolly the Sheep, transferred DNA, researchers say it could produce genetically uniform monkeys for use in research into human diseases.
But others will view it as a major step towards the creation of tailor-made humans.
Long-tailed macaques Zhong Zhong and Hua Hua were born at the Chinese Academy of Sciences Institute of Neuroscience in Shanghai using DNA from foetal connective tissue cells.
After the DNA was transferred to donated eggs, genetic reprogramming was used to switch on or off genes that would otherwise have suppressed embryo development.
Research team leader Dr Qiang Sun said: "We tried several different methods, but only one worked. There was much failure before we found a way to successfully clone a monkey.
"You can produce cloned monkeys with the same genetic background except the gene you manipulated.
"This will generate real models not just for genetically based brain diseases, but also cancer, immune or metabolic disorders and allow us to test the efficacy of the drugs for these conditions before clinical use."
Dolly the Sheep was cloned by scientists in Edinburgh 20 years ago using the single cell nuclear transfer (SCNT) technique.
It was the first time scientists had managed to clone a mammal from an adult cell.
Although a primate has been cloned before, Zhong Zhong and Hua Hua are the first using SCNT, which can theoretically produce an indefinite number of clones from a single donor.
However, Professor Robin Lovell-Badge, from The Francis Crick Institute in London, said he did not believe it increased the chances of cloned humans.
"The work in this paper is not a stepping-stone to establishing methods for obtaining live-born human clones," he said.
More from Tech
"This clearly remains a very foolish thing to attempt. It would be far too inefficient, far too unsafe, and it is also pointless.
"Clones may be genetically identical, but we are far from only being a product of our genes."