When it comes to bringing back an extinct creature, we often think first of dinosaurs.
For scientists, however, the animal to return to the land of the living is not the T. rex but Mammuthus primigenius, otherwise known as the woolly mammoth.
These hairy beasts went extinct some 10,000 years ago, but for much of the past decade, serious strides have been made to revive the woolly mammoth in some fashion. The possibility of reviving the woolly mammoth even graced the cover of National Geographic in 2013, with an illustration of the animal, along with others, walking out of a beaker.
Why are scientists focused on the woolly mammoth's de-extinction? And should we even be doing it in the first place?
We know a lot about them — but we want to know more
We know a lot about the woolly mammoth, thanks in no small part to the recency of its extinction, the careful depictions of the creatures in prehistoric cave art, and the fact that remains of the animals tend to be in remarkably good condition.
1. Woolly mammoths weren't exactly mammoth. Despite their names, male woolly mammoths could grow to be between 9 to 11 feet (2.7 to 3.3 meters) tall, not too much taller than their closest extant relative, the Asian elephant (Elephas maximus). Male mammoths weighed around 6 tons, a couple tons more than Asian elephants do today.
2. You can tell a mammoth's age by its tusks. Like tree rings but better, the rings found in a mammoth's tusks roughly indicate the mammoth's age. Layers could provide a sense of a mammoth's age even down to the day. Thicker rings indicated that the mammoth was quite healthy and growing quickly, while thinner rings meant the mammoth was likely growing at a slower pace.
3. The outer hair of mammoths could grow to be a foot or longer, with a shorter undercoat. It was the ice age after all, so keeping warm was a must. The mammoths' coat of hair could be up to 35 inches (90 centimeters) long. The undercoat, which would be curlier and thinner than the outer coat, would have hairs up to 3 inches long. The hairs we have found have been orange, but there's a possibility that being buried under the ground for so long changed their color.
4. Mammoths were an important part in the lives of early humans. During the Pleistocene epoch, which began 1.8 million years ago and ended 10,000 years ago, mammoths were used by early humans for a variety of purposes. Mammoth meat was used for food, the creatures' coats were used for clothes and their bones and tusks helped humans to build their huts. Mammoths feature prominently in early human art. We've found sculpted figures of mammoths, and the beasts appear 158 times in France's Rouffignac caves.
5. We've discovered many, many mammoths over the centuries. By the late 17th century, descriptions of frozen mammoths were circulating in Europe, though no complete skeletons were recovered. In 1799, a hunter discovered a frozen mammoth, allowing it to thaw until he could gain access to the tusks. This same specimen was later collected as the most complete skeleton at the time in 1808. Since then, many mammoths have been discovered, including calves, in many places around the world, including Michigan.
Bringing back the dead
Bringing the mammoth back from extinction isn't an easy task. The two ways in which scientists have thought to tackle this problem have either been through cloning or the modification of Asian elephant genes using genes from a woolly mammoth (the woolly mammoth's genome was sequenced in 2015).
Cloning a mammoth was the first way scientists thought to bring the mammoth back. Back in 2011, a team of scientists from Japan, Russia and the United States were reportedly working together to clone a mammoth. According to CNN, the plan was to use DNA extracted from a mammoth carcass preserved in a Russian lab and insert it the egg of an African elephant. The goal was to create a mammoth embryo this way by 2016.
There hasn't been much progress made with this approach, however. One potential reason is that the freezing process doesn't stop the cell death. It may slow down the process, but a few thousand years will still break cells apart. "Ten thousand years of radiation. In a frozen specimen that has no metabolism going on, it's accumulating and breaking into bits," George Church, a professor of genetics at Harvard Medical School, told The Washington Post in 2015. "That DNA will never function again."
Church has been involved in the process of bringing back the mammoth, too, albeit in a more scaled back way than outright cloning. Relying on the sequenced genome, Church's project seeks to bring about a "proxy" species to the mammoth, one that shares some traits and functions of the woolly mammoth. To achieve this, Church's team is carefully placing the genes of woolly mammoths into the cells of Asian elephants. As of 2018, they have made more than 40 changes to the Asian elephant using CRISPR, the gene-editing technology.
The mammoth genes have mostly focused on those that would allow the proxy species to thrive in cold weather, specifically mammoth hemoglobin, which allows blood circulation even at low temperatures, woolly hair for protection against the elements and the development of more fat for insulation and fasting. Once these traits appear sufficiently in stem cell-derived tissues, researchers will begin experiments to create embryos. They hope to place these embryos in artificial uteri, eliminating the need to use an Asian elephant as a surrogate for this woolly proxy.
To de-extinct or not de-extinct?
Beyond the scientific questions of bringing back a creature that has been extinct for 10,000 years, there's the ethical questions about the process and the goal.
For Church and others, the issue of de-extinction is one part of combating climate change. Returning mammoths to their historic ranges, particularly the tundras and forests of northern latitudes, could return these regions to grasslands. Russian ecologist Sergey Zimov argues that bringing grazers like mammoths back will trigger a cycle in which grasses will be able to outcompete tundra flora.
The reason this matters is that grasslands are likely to sequester carbon from the atmosphere better than other land types, but especially tundras. Additionally, grasslands may enable deeper freezing of permafrost during the winter months and insulate it during the summer months, a way of preventing the release of any captured emissions.
Of course, this is only supposition since we can't know for sure how a new version of the mammoth would behave, or how we would ultimately care for it while it's maturing. Additionally, as Helen Pilcher, a cell biologist writing for the BBC explained in 2017, it would take a long while for the mammoths to be able to achieve this goal.
"Even if all the technical hurdles involved in making a mammoth were overcome tomorrow, it would still take well over half a century to make a single viable herd, which would not be anywhere enough to do the job," Pilcher wrote.
"Instead, by that time, if current predictions are to be believed, the Arctic permafrost will already have melted. What's more, the Siberian ecosystem may have changed too much and may be unable to support the new arrivals."
Resurrecting the mammoth does have some benefits, however, albeit indirectly. Pilcher believes the techniques involved in trying to bring back the mammoth could help living species, especially those that are threatened or endangered, making the project ultimately worthwhile. The organization that Church leads, the Revive and Restore Project, is already working on ways to help the black-footed ferret in North America survive years of inbreeding.
The de-extinction of the mammoth could bring about more biodiversity, but some conservationists worry that it could also set a precedent that would undermine efforts to keep species alive.
"De-extinction just provides the ultimate 'out'," Stanley Temple, a wildlife biologist at the University of Wisconsin-Madison, told BBC Newsbeat in 2015. "If you can always bring the species back later, it undermines the urgency about preventing extinctions."