Cloning Woolly Mammoths: It's the Ecology, Stupid

Scientific American
Cloning Woolly Mammoths: It's the Ecology, Stupid
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Artist's rendering of woolly mammoths.

As an ecologist of ice age giants, I long ago came to terms with the fact that I will never look my study organisms in the eye. I will never observe black-bear-sized beavers through binoculars in their natural habitats, build experimental exclosures to test the effects of mastodons on plants, or even observe a giant ground sloth in a zoo.

As a conservation paleoecologist, I study the natural experiments of the past--like climate change and extinction--to better understand the ecology of a warming, fragmented world. Admitedly, part of the appeal of the ice age past is the challenge of reconstructing long-disappeared landscapes from fragments like pollen, tiny fragments of charcoal, and bits of leaves preserved in lakes. In the absence of mammoths, for example, I rely instead on spores of fungi that once inhabited their dung.

De-extinction could change that. On Friday, a group of geneticists, conservationists, journalists, and others convened in Washington, D.C. to discuss resurrecting extinct species, including the woolly mammoth. De-extinction sounds like science fiction, but it's rooted in very real conservation concerns. With the sequencing of the woolly mammoth genome complete and recent advancements in biotechnology, the question of whether to clone extinct species like mastodons, dodos, or the Shasta ground sloth is rapidly becoming more of a question of should, rather than how. The latter isn't straightforward, and involves the integration of a number of cutting edge disciplines, but I'd like to focus on the former: should we clone woolly mammoths?

A growing problem I've had (and one which Brian Switek raises in a recent post at National Geographic) is that the de-extinction proposals are Big Ideas, but they they're often shallow when it comes to ecology. Even the concept of "de-extinction" itself is misleading. Successfully cloning an animal is one thing; rescuing it from the black hole-like pull of extinction is another. Decades of conservation biology research has tried to determine the careful calculus of how many individuals and how much land are needed for a species to survive without major intervention, accounting for its needs for food, habitat, and other resources.

Mammoths have been extinct on continents for over ten thousand years (though dwarf versions survived into the time of the ancient Egyptians on isolated Arctic islands). Even so, the fossil record has yielded rich clues about ecology. All ethical considerations aside, from a conservation biology standpoint, what does it mean to be a mammoth?

The woolly mammoth is the ice age species with the best-preserved specimens, and it was the first to have its genome sequenced (though the Neanderthals followed in 2010). As far as de-extinction efforts go, it's likely to be one of the first successful cloning efforts.

However, not all mammoths were woolly tundra-dwellers; in North America, mammoth remains have been found at elevations ranging from sea level to the mountains of the Colorado Plateau, and from Canada to central Mexico. The largest of these, the Columbian mammoth, dwelled in savannas and grasslands like African elephants today, and the smallest--Pygmy Mammoths--lived on the isolated Channel Islands off the California coast.

While knowing their habitat alone is useful in terms of identifying potential cloned mammoth reserves, we do in fact know quite a lot about what mammoths ate. Based on plant materials found in fossilized dung, the contents of permafrost-preserved stomachs, and isotopes in teeth enamel, we know that most mammoths were grazers, preferring grasses and herbs to woody trees and shrubs.

In this way, mammoths were similar to modern African elephants, though evolutionarily they're more closely related to the forest-dwelling Asian elephants. Unlike horses and camels, which evolved in North America, mammoths were relatively recent comers, arriving around 1.7 million years ago via the same land bridge that the first humans would later take during the last ice age.

Mammoths likely had elaborate social systems similar to modern elephants, and are thought to have lived in groups of up to twenty individuals. Woolly mammoths males had musth glands, which are important in modern elephant reproduction today. Groupings of mammoth bones at sites where multiple individuals died together show extended family structures. Preserved mammoth tracks show extended families walking side-by-side, as well as a decline in juveniles that indicate populations were in decline due to human hunting.

Just like modern elephants today, these groups were all females, and so it's likely that mammoths were also matriarchal. Groups of females would typically stay together, and males would have been kicked out of the herd and left to fend for themselves when they reached adolescence.

How could we possibly know this? The fossil record shows that mammoth tusks grew rings--just a like a tree, except mammoth tusks can record weeks or even days in a mammoth's life. From the width of rings and their isotopic makeup, we know that mammoth mothers nursed their young for two or three years. In teenage males, the growth rings in the tusks become suddenly narrow, indicating that the male suddenly had to fend for itself (the equivalent of going from your parents' home-cooked meals to the macaroni and cheese and ramen diets of your first apartment).

Not all teenaged mammoths survived this dangerous period of isolation; at the Hot Springs Mammoth Site, paleontologists have uncovered a number of single, adolescent male skeletons that fell in the sinkhole and perished, one after the other through time. Broken tusks also reveal that, just like modern elephants, mammoth males fought for mates--there's even a pair of male skeletons locked in eternal combat, unable to disentangle themselves.

Modern elephants have elaborate communication systems involving touch, sight, chemistry, and sound (including infrasonic and seismic communication across long distances). While fossils cannot recapture the sound of a mammoth's trumpet call, but we do know from modifications in their hyoid bones, tongue, and voice box that they would have been capable of low frequency communication, too.

The mammoth steppe is just as extinct as its namesake, due to a combination of climate change and the loss of those megaherbivores that were likely "keystones," ecological engineers of their own habitats. Assuming that parts of modern Siberia or boreal Canada would do, how much land would a woolly mammoth need? The science on this is much less clear. By matching the isotopes in tooth enamel with the isotopes in soils, we know that some species of mammoths and mastodons roamed as much as 500 km a year, perhaps migrating to track their habitats.

Calculating the carrying capacity of a mammoth herd is not trivial (trust me--I'm working on it!), and involves a careful consideration of how much forage mammoths would need to consume (modern elephants eat as much as 440 pounds a day), proximity to water (modern elephants drink around 60 gallons daily), and the complex interaction between animals, plants, and the changing climates they experienced as their populations dwindled. Once we know how much land a mammoth herd needs, it's another matter entirely to determine how many of those herds are necessary to maintain viable populations of woolly mammoths in the wild. Whatever that number may ultimately be, it's worth pointing out that 14,000 years ago, it only took small bands of spear-wielding humans and a backdrop of changing climates to push mammoths and other ice age megafauna over the brink.

When we think of cloning woolly mammoths, it's easy to picture a rolling tundra landscape, the charismatic hulking beasts grazing lazily amongst arctic wildflowers. But what does cloning a woolly mammoth actually mean? What is a woolly mammoth, really? Is one lonely calf, raised in captivity and without the context of its herd and environment, really a mammoth?

Does it matter that there are no mammoth matriarchs to nurse that calf, to inoculate it with necessary gut bacteria, to teach it how to care for itself, how to speak with other mammoths, where the ancestral migration paths are, and how to avoid sinkholes and find water? Does it matter that the permafrost is melting, and that the mammoth steppe is gone? As much as I love mammoths, the ecologist in me can't help but answer: no.

These are practical considerations as much as they are as philosophical ones. Human activity is pushing the earth system outside of the natural range of climate variability that mammoths of all species--woolly or otherwise--would have experienced during their evolutionary history. Ironically, much of what we know about mammoth ecology comes from the newly-exposed carcasses uncovered from the melting permafrost.

There are compelling ecological reasons to resurrect extinct species. Some have argued for rewilding to maintain certain habitats or to perform important functions like seed dispersal or fire suppression. As I've written previously, many plants live today as ecological anachronisms, out of context with their extinct dispersers. Bringing back the passenger pigeon may be an important part of saving the sand cherry (or even the American chestnut).

My research on the ecological consequences of the extinctions of mammoths and other megaherbivores in North America indicates that the loss of mammoths during an interval of rapid climate change led to completely novel communities--a period of ecological upheaval that lasted for two thousand years. Work by others suggests that there may have been cascading effects to the biodiversity of small mammals. Modern elephants are keystone species, helping to maintain the African savanna habitat that many other species rely on.

Losing species--especially ecosystem engineers, foundation species, or keystone herbivores, can lead to cascading effects that can be difficult to predict. The reverse is also true; adding herbivores to landscapes changes them. Are we--is society--prepared to accept those changes?

I understand the impetus to resurrect the woolly mammoth--it comes from that same sense of wonder and drive for discovery that led me to be a scientist in the first place. When I watched 10,000 BC, I admit that I wept openly at the sight of CGI mammoths on the big screen. I would be the first person on a plane to Siberia if mammoths showed up in Pleistocene Park. Science needs icons--rallying points that capture the public interest. Cloning a woolly mammoth could be the equivalent of the moonwalk for biology, resurrecting not just an extinct species, but also rekindling a child-like sense of excitement for the natural world (though admittedly, cloning's public opinion record has tended to be more one of fear and admonition that scientists are "playing God"). And yet, as Hannah Waters rightfully points out, cloning extinct species may actually be more about us humans than the wildlife we care about.

Arguments against de-extinction often center around what we don't know--particularly when it comes to the long-term collateral effects of our actions. The precautionary principle can be unsatisfying in conservation, because taken to its logical extreme it precludes action of any kind. We often don't have the luxury of waiting to determine how effective an action will be, especially as we race to save species on the brink of extinction.

In the case of mammoths, however, there need be no sense of urgency. Perhaps the best course of action is to first demonstrate that we can effectively manage living rhinos and elephants before resurrecting their woolly counterparts in a warming, fragmented, overpopulated world.

Ultimately, cloning woolly mammoths doesn't end in the lab. If the goal really is de-extinction and not merely the scientific equivalent of achievement unlocked!, then bringing back the mammoth means sustained effort, intensive management, and a massive commitment of conservation resources. Our track record on this is not reassuring.

In the meantime, the least we can do is be guided by what we do know about woolly mammoths in their ecological context. Before we talk seriously about de-extinction, let's apply the lessons of the woolly mammoth to help save species in the face of pre-extinction.

Images: Ice age fauna of northern Spain by Mauricio Ant?n at Wikimedia Commons; A Mammoth Skull by Robert Geier; Elephants at Amboseli national park against Mount Kilimanjaro by Amoghavarsha at Wikimedia Commons; Three elephant's curly kisses by jinterwas at Flickr.

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