Two teams of researchers have apparently gone on record as saying they plan on cloning the mammoth. In 2008, when the mammoth genome was announced in the journal Nature, we took at look at that possibility, and concluded it wouldn't work. Given the recent press attention, we thought we'd rerun an updated version of the relevant section from our original report.

Given that the genome is often called the blueprint for an organism, Nature took the liberty of commissioning an evaluation of what it would take to rebuild the mammoth using that blueprint. The challenge is enormous: each one of the mammoth's chromosomes are likely to be over 100 million base pairs long; the average surviving fragment of DNA we've obtained from mammoth remains is under 200 bases long.

That means the sort of cloning technique that we use on currently living mammals wouldn't work, since it relies on a genome that's largely intact. The cloned cells can undoubtedly repair some DNA damage, but nothing like the scrambled fragments we have from mammoths. There's always the chance that some mammoth remains contain larger fragments of DNA, but basic chemistry indicates that we're unlikely to ever find anything close to an intact chromosome.

So the piece suggests starting from scratch, using a process similar to the one that constructed the first artificial genome. Unfortunately, that bacterial genome is about three orders of magnitude smaller than a single mammoth chromosome, and the techniques used are simply unlikely to scale. Mammoths also had dozens of chromosomes, and we'd need to get two copies of each into a single cell, safely encapsulated in a nucleus. We've only got techniques that work for some of this, and we've never tried any of the ones that work on a task approaching this scale.

Assuming we have two full sets of mammoth chromosomes together in a single nucleus, advances in stem cell research suggest we could reset them to an embryonic stem cell state using molecular tools. Unfortunately, we still don't know how to get these stem cells to develop into adult organisms without implanting them into a viable egg or embryo. That would mean we'd need the embryo of a closely related species to work with.

It would obviously be best to do this with elephants (as the teams of researchers have realized), both as egg donors and surrogates. But, apparently thanks to an aquatic lifestyle in the elephant's evolutionary past, they have a baroque reproductive tract and an internal organ arrangement that makes laparoscopy to harvest eggs a non-starter. So, the elephant represents yet another technical hurdle.

There are a host of other issues that are relatively minor in scale—we'd need a Y chromosome and sequence from enough individuals to create a diverse breeding population—but resurrecting the mammoth faces some technological obstacles that we haven't yet even started to try to overcome. A more likely solution, Nature concludes, would be to identify the regions of the genome that have diverged most significantly between elephants and mammoths, and engineer the mammoth equivalent back into an elephant's DNA. Depending how well we can identify these, the mammophant that we produce may be at least physically indistinguishable from artists' renderings we're all familiar with.

Overall, Nature's analysis is pretty persuasive. Given the technology we have now, it's tough to imagine putting a mammoth together, even given the complete genome sequence.

But it's difficult to predict how technology advances will proceed. The article quotes one of the researchers who lead the efforts to sequence the Neanderthal and Denisovan genomes, Svante Paabo, as saying he doesn't expect to see anything more than a mammophant in his lifetime. Of course, Paabo's in his 50s, and I'd imagine that, in his 20s, he wouldn't have expected to see a Neanderthal genome completed in his lifetime. He has done just that.

Nature, 2008. DOI: 10.1038/456310a