These problems might be avoided if we could find intact nuclei from frozen mammoths, at least if experiments in other animals are anything to go by. In 2008, Sayaka Wakayama and colleagues from RIKEN, Japan cloned healthy mice from individuals that had been frozen for 16 years. They found intact nuclei in the chilled bodies, and fused them with empty eggs. By all accounts, Iritani is trying to do the same thing with frozen mammoth remains (he did not respond to a request for an interview). But Schuster does not mince words about the odds of finding intact mammoth nuclei. “It’s entirely impossible,” he says. Sixteen years in the freezer is one thing; 16,000 years is quite another.
Pregnant pause
Assuming that Iritani’s team gets an intact nucleus, they would still have to insert it inside an elephant egg. Collecting such an egg means navigating a reproductive tract that spans three metres from the uterus to the outside world. “It’s extremely challenging,” says Thomas Hildebrandt from the Leibniz Institute for Zoo and Wildlife Research, who knows the reproductive tract of elephants like the length of his arm.
A female elephant only ovulates once every five years, releasing one or two eggs at any time to ensure that she never becomes pregnant with several gargantuan foetuses. Each egg is a 2-centimetre-wide ball rattling around an enormous cavern. Once it is released, the female almost immediately has sex. “There are almost no wild elephants that are fertile without already being pregnant,” says Hildebrandt. So, collecting an oocyte from an elephant is like groping in a haystack for a needle that probably does not exist. If getting one egg sounds hard enough, would-be mammoth-makers need hundreds or thousands of eggs to ensure one successful clone.
There is a possible cheat. They could take ovarian tissue from a culled elephant, transplant it into a rat or a mouse, and tweak the rodent’s hormonal cycles to ensure that the eggs mature properly. This has been tried, but no one knows if the resulting eggs were actually viable. It’s a long shot, and “you still have the problem of transplanting the embryo,” says Hildebrandt.
Notwithstanding the distance into the uterus, the path is blocked by the hymen. This is essential to the elephant; it grows back after every birth and it cannot be broken without compromising the pregnancy. It has an opening just 2 to 4 millimetres wide that allows passage to sperm – that’s what an embryo-carrying tube would have to navigate through. “It’s not impossible but it would need quite a lot of technological development,” says Hildebrandt. “Most people don’t expect that. They think they biggest challenge is creating the embryo.”
Even if a baby mammoth comes to term, it may not last for long. In 2009, European scientists used preserved skin cells to clone the Pyrenean ibex, a type of goat that had been extinct since 2000. The glorious resurrection lasted all of seven minutes, before the newborn kid died of lung failure. Many (but far from all) cloned animals have suffered from similar health problems. If the woolly mammoth does the same, its resurrectors could end up with the world’s most expensive carcass.
Conservation boost
Despite these many hurdles, Schuster does not dismiss the possibility of cloning a mammoth, especially with improvements in genetic techniques. “Every time a journalist asks me about this, one of those hurdles has been taken out,” he says. “I think it’s a little irresponsible to stand there and say it’ll never happen, but that doesn’t mean we should spend money on it. Maybe it would be better spent on preserving endangered species today.”
