Since Jurassic Park, de-extinction, the process of generating an organism that is either an extinct species or resembles an extinct species, has been an intriguing prospect. The concept of bringing back the woolly mammoth, for example, has been a well-mooted topic for decades, with recent technological improvements turning what was once just a romantic fantasy, into a feasible possibility. Mammoth bones recovered from perilous tundra in northeast Siberia provide the basic ingredient for this ambitious undertaking.
Historically, Siberian sub-zero temperatures have significantly slowed the decomposition of organic materials left frozen in the permafrost for millennia (Mezrich, 2017), including that of the woolly mammoth. DNA degrades over time, thereby hampering efforts to sequence a mammoth’s entire genome, and consequently eliminating cloning as an option (Shapiro, 2015). But it is now possible to stitch various fragments of preserved DNA together to form a near-complete genomic model using CRISPR technology, which enables precise editing of DNA within a living organism. Or, in this context, DNA within a close living relative (Rich, 2020).
George Church, head geneticist on the Harvard “Mammoth Project”, is leading the team tasked with bringing it back, having already successfully synthesised a number of elephant genes in vitro, generating increasingly mammoth-like cells with each precise edit (Anon., 2021). While 99% of a mammoth’s genome is very similar to that of the Asian elephant (Worrall, 2019), Church is in the process of comparing the Asian elephants’ genome against the model mammoth’s, to identify the genes that need synthesising. The goal is to reintroduce the traits that make a woolly mammoth unique and able to thrive in the sub-Arctic tundra; subcutaneous fat, small ears, a shaggy coat and, importantly, haemoglobin to maintain their high metabolism (Knapton, 2015). Once spliced, the next step is somatic-cell nuclear transfer of the reconstituted genome into the enucleated zygote of a donated elephant egg (Brand, 2014). The final step in creating a mammoth calf requires the construction of an artificial uterus to gestate the embryo (Sarchet, 2017), from which it will ultimately be born.
Scientists are confident that bringing back the mammoth is plausible, but given the exorbitant costs associated with such an endeavour, it is reasonable to ask whether the investment is genuinely worth it.
Trampling greenhouse gas emissions
Climate change and biodiversity loss are the greatest threats humanity has faced since its appearance on Earth 7 million years ago (Attenborough, 2021). The planet has warmed by over 1°C since pre-industrial levels and is currently on track for a 4°C increase by the end of the century (WMO, 2020). The effects on the planet will be catastrophic, not least in Siberia where a thick layer of permafrost, or frozen soil, has started to thaw.
Permafrost contains over 1600 billion tonnes of carbon, twice the carbon currently in the atmosphere and three times the carbon sequestered in the world’s forests (Schuur, 2019). As the soil thaws, these carbon-rich vestiges of ancient life, including plant roots and animal carcasses, are released and converted into carbon dioxide and methane by hungry microbes. Scientists predict that at current rates, 2.5 million square miles of permafrost – 40% of the world’s total – could disappear by the end of the century (Chadburn, et al., 2017), using up to ¼ of the carbon cap set in the Paris Accord (Anon., 2020); this is a slug of the budget we can ill-afford to lose.
Pleistocene park covers 160km2 of perilous tundra in northeast Siberia and forms the basis of Russian scientist Sergei Zimov’s unconventional plan to slow the thawing of the permafrost (Zimov, 2005). Zimov believes he has the answer to averting this potential climate catastrophe; he says, “there is only one [way] to prevent [this] from happening. We must restore the Ice Age.” By reintroducing heavy grazing animals, a feature of the “Pleistocene epoch”, a blanket of metre-thick insulating snow is trampled, making it dense and more able to allow extreme winter cold to penetrate the soil underneath (Wernick, 2017), thereby slowing the thawing of the permafrost.
But trampling the snow isn’t the only benefit grazers offer. They also generate a nutrient cycle that favours grasslands over the current tundra flora, a landscape peppered by coniferous trees. Whilst nurturing grasslands at the expense of trees may seem counter-intuitive in the fight against climate change, in the context of snow-covered arctic tundra, the environmental benefits heavily outweigh the costs. Trees may well be good carbon sinks, but they also absorb heat which ultimately warms the permafrost beneath them. Grass on the other hand, reflects more light and thus reduces the amount of heat absorbed by the soil, whilst also capturing more carbon in its roots than current vegetation. In turn, the grasses can feed huge armies of herbivores – a beautifully harmonious ecosystem.
Following the introduction of reindeer, bison, musk ox and yak, Zimov’s early trials are promising: the temperature of the permafrost in Pleistocene park is now 2.2°C lower than before (Anon., 2020). But without powerful tree-felling herbivores, like mammoths, to trample shrubs and uproot trees, Zimov has had to deploy tanks in their place. Such a drastic approach to tree management is fine to prove its effects but, in the long run, it is unrealistic and unsustainable for a landmass the size of Siberia. 30,000 years ago the mammoths’ extreme bulk and voracious appetites crushed trees before they had the chance to grow and spread (Anon., 2020). This thinning of park woodland is evident today, for example in South Africa’s Kruger National Park, where a rising elephant population has kept tree numbers down (Anderson, 2017). Rather than a fleet of gas-guzzling bulldozers, the reintroduction of climate-friendly, tree-felling mammoths could be the solution.
Honing conservation efforts
While slowing the thawing of the permafrost is the key incentive driving research into mammoth de-extinction, there are other valuable benefits too. The insights gained from genetic rescue can expedite our ability to conserve wildlife currently threatened by climate change in a variety of ways:
- Increasingly endangered species, by definition, have ever smaller remnant populations which inevitably results in progressive inbreeding. This drives a loss of fecundity due to increased homozygosity of deleterious genes and, as is the case for any organism, a plummeting population results in significant loss of valuable alleles. Consequently, these species lack the genetic diversity to adapt effectively, and become more susceptible to diseases (Quill, 2015). Developments in gene-editing technology could allow the restoration of heterozygosity in living genomes and potentially even revive the “extinct”, valuable alleles from fossils, both of which would re-establish genetic diversity and provide the adaptive robustness necessary for the species’ survival (Brand, 2014).
- The synthetic construction of the mammoth genome provides scientists with a historic record of millions of years’ worth of adaption against catastrophes, epidemics and changing environments. Reanimation of genes in living cells can identify how past populations dealt with these changes in ways that studying genetic code alone could not. This information might then be utilised using CRISPR, to facilitate a species’ synthetic adaptation to climate change, or confer disease resistance in species with small remnant populations (Anon., 2021).
- Plans to grow the hybrid mammoth-elephant embryo within an artificial womb (Delvin, 2017) involve extensive assisted reproduction. Given the size of the calf and lengthy gestation period (estimated to be over two years (Pilcher, 2017)), de-extinction of the woolly mammoth would significantly push the current limits of advanced reproductive technologies, which could significantly benefit the survival of crucial megafauna species across the globe (Anon., 2021).
Obstacles facing de-extinction
While the case for mammoth de-extinction is robust, not everyone is convinced. Sceptics argue that even after successful genomic editing and assisted reproduction, other factors make it unlikely that mammoths will flourish again. Poaching, for example, is a major problem for many of the world’s largest mammals and there is already a highly lucrative, albeit legal, market for mammoth tusks that can be found in the thawing permafrost; it is inconceivable to think poaching wouldn’t threaten the longevity of the mammoth.
Mammoth reintroduction may also flounder as they could find it difficult to survive in today’s Siberian ecosystem, one that has changed significantly since the Pleistocene epoch. Mammoths largely fed on grasslands that once spanned Siberia, Alaska and much of Canada’s Yukon (Anderson, 2017). 10,000 years ago, however, this vast system known as the Mammoth Steppe disappeared completely, and was replaced by mossy, forest tundra, and the mammoths disappeared along with it (Zimov, 2005). Without nutritious grasslands to fuel their demanding metabolisms, it is unlikely a battalion of 21st century mammoths would survive.
Sceptics also note that in the early stages of mammoth reintroduction, calves would have no role models from which to learn the life skills needed to survive in the wild. Young mammoths would need to learn, for example, what to eat and how to find it, including the essential task of felling trees. Zoologists have found it very difficult to reintroduce captive megafauna, such as elephants, into the wild (Cormier, 2018), so the prospect for successful role-model training for mammoths seems dim.
Factors weakening the value of de-extinction
Feasibility aside, the question of whether they should return remains. The funds required for genetic rescue might be better spent on other environmentally critical projects. For example, projects that prevent the extinction of currently endangered species, climate change mitigation strategies (such as investments in carbon capture, advancements in renewable energy technology and more efficient transportation) or projects that slow human population growth.
Furthermore, the risk of negative unintended consequences of mammoth de-extinction might be problematic; bringing back a previously extinct species, especially one as compelling as the woolly mammoth, may mean people become more blasé about the loss of the millions of species currently on the brink of extinction. There could be even less collective drive to stem the fast approaching sixth mass extinction.
Giving mammoths the green light
Mammoth de-extinction is undoubtedly a controversial topic, but its benefits outweigh its costs. The threat posed by climate change on humanity are very real and imminent. Studies suggest that climate change could cause the extinction of one-third of all plant and animal species within 50 years (Cockburn, 2020). The resulting biodiversity loss would pose innumerable risks to human welfare, including increased outbreaks of infectious diseases (Watts, 2021); reduced security of the world’s food supplies (FAO, 2019); and decreased access to clean, fresh water and good quality air (Dias, et al., 2012).
In addition to advancing our ability to conserve species currently on the brink of extinction and given that thawing of the permafrost would use up to ¼ of our carbon budget, we have no choice but to invest in projects that may prevent the release of these greenhouse gases, however far-fetched they may seem. Human ingenuity, for example using a fleet of bulldozers to selectively clear trees from the Siberian landscape to allow grassland to flourish prior to the introduction of the mammoths, can overcome any obstacle that might limit the project’s long-term success. Without a viable alternative, bringing mammoths back from the dead could be an opportunity we would be ill-advised to miss.
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