The news that South Korean scientists are planning to clone a mammoth, using the DNA of a particularly well-preserved specimen in the Siberian permafrost, has reignited the debate over the ethics of cloning. But whether or not it's right, could it happen? And what other animals could, or couldn't, we clone?
It may be possible to clone a mammoth. It would be an enormous technical challenge, because the freezing process which preserves the dead animals also tears up the cells. Normal cloning techniques - such as that which produced Dolly the Sheep - involve taking the whole cell from the animal being cloned, and allowing it to divide in a petri dish with an egg cell which has had the DNA removed. When the cell is torn apart by the ice crystals which form during freezing, that can't work.
However, scientists have successfully cloned a mouse which had been frozen for 16 years by using a different technique: taking the DNA-containing nucleus out of the cell to be cloned, and injecting that directly into a denucleated egg cell. That suggests that, in principle, the same could be done for a mammoth.
However, there are huge obstacles: for a start, the DNA will have degraded over the millennia since the mammoth was frozen, and while the scientists could freeze as many mice as they liked and use thousands of cells for their purposes, there is an extremely limited number of mammoths available to work with.
It may be possible to use the undamaged parts of DNA that can be found and insert them into the genome of a modern elephant, which shares 99.4 per cent of its DNA with the mammoth.
Neanderthal
A lifelike figure of a Neanderthal Man in the Neanderthal Museum in Germany. (Photo: Alamy)
But while the technical challenges of cloning Neanderthals are roughly the same as those of cloning mammoth - frozen cells, degraded DNA - in the case of Neanderthals, the ethical problems become practical problems as well. The cloning process - even for modern animals, such as Dolly - usually involves lots of failures, sometimes failures which make it all the way to birth.
Dolly herself was one of 29 embryos, and the only one to survive, as Alex Knapp writes in a piece on the subject in Forbes. People may just about accept that when it is an elephant giving birth to unviable mammoth babies, but the idea of dozens of women giving birth to dead, dying or disabled Neanderthal babies in the name of science simply will not happen.
Pyrenean ibex
A Pyrenean ibex. Sketch by Joseph Wolf, from the book 'Wild oxen, sheep & goats of all lands, living and extinct' (1898) by Richard Lydekker
The only extinct animal that has been successfully cloned - but that really is using the term "success" very loosely indeed. The Pyrenean ibex went extinct in 2000. In 2009, a clone made from DNA recovered from Celia, the last surviving specimen, was born alive. But the clone had profound defects in its lungs, and died less than 10 minutes later. None the less, given the money and resources, it is plausible that future efforts would be successful.
Tyrannosaurus rex
A T-rex: completely unclonable. Sorry. (Photo: Christopher Pledger)
Never going to happen, and nor is any other dinosaur. The problem of DNA degradation discussed when we were talking about mammoth is bad enough when you're dealing with a timescale of thousands or tens of thousands of years. DNA has a "half-life" of about 500 years, according to research carried out at universities in Copenhagen and Perth, meaning that only half of any sample is usable after that time.
You can still theoretically piece together a genome from the parts of several cells for quite a long time - but the researchers reckon 6.8 million is the absolute limit, by which time essentially every single bond along the strands of DNA will be broken. The practical limit will probably be hundreds of thousands of years, not millions. T-rex and the rest of the most recent dinosaurs (apart from the ones that later became birds) were wiped out by an asteroid or comet hitting the Earth on what is now the Yucatan peninsula in Mexico, 64 million years ago.
There will simply not be any usable genetic material. Jurassic Park, sadly, will remain fiction.
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