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Two cloned macaque monkeys are sex c?a ?n ??presently exploring the confines of an incubator, built for human babies, inside a research laboratory run by the Chinese Academy of Sciences.

Primates have been cloned before, but this is the first time monkeys were duplicated using the same technique -- called somatic cell nuclear transfer --that scientists used to clone Dolly the sheep, in 1996.

Beyond the obvious scientific achievement -- whose results were published today in the journal Cell-- the important advancement here is that these scientists plan to produce more cloned monkeys in the coming months, and believe they can make primate cloning relatively cheap. The scientists underscore that these genetically identical animals, akin to identical human twins, are to be used only to advance human medicine.

"Monkeys are non-human primates that evolved close to humans," said study co-author Mu-ming Poo, who is the director of the Institute of Neuroscience at the Chinese Academy of Sciences, during a call with reporters. "Thus, they’re ideal models for studying human diseases and developing medical treatments."

Today, new human medicines are regularly tested on critters like mice or in test tube conditions (also called "in vitro"), but Moo believes cloning animals -- specifically those genetically close to us -- is necessary.

"I’m personally not confident that we can produce really good medical treatments without testing real animals," said Moo.

The two cloned female monkeys, who are six and eight weeks old, are not being experimented on right now due to their young and fragile state, said Moo. They're also being kept in the closely-monitored incubator away from their surrogate mothers (which carried the cloned embryos) because Moo is "concerned surrogate mothers will not take care of them well."

The benefit in producing cloned monkeys (or any animal) is that they share the exact same genetic make-up, which would give researches a uniform set of animals from which to test new drugs. For instance, if a lab had 10 cloned monkeys, it could give five of them an experimental medicine, and give the others no treatments (the control group). The results of the treatment would ostensibly give researchers clearer answers about whether or not a treatment, perhaps for a form of cancer, worked.

But other researchers are not so sure cloning monkeys -- which is an inherently expensive and ethically controversial undertaking -- is necessary.

"The thing is, it is very expensive research and you need a really good justification to clone 20 monkeys," said Hans-Michael Kubisch, a genetic researcher who previously managed the breeding of rhesus monkeys at the Tulane National Primate Research Center, in an interview.

"There might be some research that’s desirable to have monkeys that are all alike, but I think it would be exceptional circumstances," said Kubisch.

Moo estimated that cloning a monkey could cost around $50,000, but he didn't give details about how he arrived at this number -- and it's unlikely this includes the costs of maintaining a colony of intelligent, cloned creatures to be used in animal studies.

"I would argue there are other animal models that are less expensive than monkeys," said Carol Keefer, who researches embryonic development and stem cells at the University of Maryland.

Even if a well-funded government or university lab did buy a group of cloned monkeys from the Chinese Academy of Sciences, it's not as if this would create a completely ideal laboratory model.

"Monkeys are closer [to humans] than pigs, but even then it's not going to be a perfect," said Keefer.

With this type of cloning technique, Keefer noted that researchers can give all the clones a specific type or variant of a gene, perhaps one that causes an incurable disease like cystic fibrosis. This would allow scientists to test novel medicines on the animal, to see how they work, "so you can make claims about the effectiveness of a drug," he said.

Giving intelligent primates a genetic disease for the benefit of testing human medicine would be rife with controversy, especially in the U.S, which has banned biomedical testing on chimpanzees.

But Moo thinks Western countries will come around to the idea of cloning monkeys for medical research. He recognized that "the public sentiment against the use of monkeys is in Europe and the United States," but expressed hope that Western countries "will gradually change their mind" and accept monkeys as a useful medical species.

Moo also noted that his lab has no interest in cloning humans, stating there is "no intention to apply this method to humans."

If the human persuasion of primate were ever cloned, Keefer makes the important point that these clones wouldn't simply be medical "models" in a laboratory.

"That wouldn’t be a model," she said. "That would be a patient."