The woolly mammoth is inarguably the mascot of the Ice Age. With countless depictions in popular culture, one would be hard pressed to find someone unfamiliar with the hairy giant herbivore. Alas, the mammoth has been extinct for thousands of years, surviving in low numbers on some islands North of Alaska until as recently as 4000 years ago but mostly dying off during the Pleistocene meltdown—a period of global climate warming marked by glacial receding. The legacy of the mammoth is captivating and their sudden disappearance continues to inspire a host of questions. What makes these animals standout as the source of modern fascination and scientific inquiry? What can their genomic information tell us about their extinction? And is it possible to resurrect the beast with this information? These and other queries have been considered by some of today's top scientists.
From the numerous cave paintings in France to discovery of tusks and even half-decayed bodies, our world is still riddled with the images and remnants of the woolly mammoth. In a quirk of modern climate change, mammoth ivory is now being traded out of Siberia, where the permafrost is relinquishing its grip on ancient troves of buried tusks, and their legacy is kept in tact through their closely related cousins, the African and Indian elephant. Due to the accessibility of their remains and access to such closely related modern cousins, mammoths have been the subject of the most extensive genome investigation of any extinct megafauna and inspired collaborations like the Mammoth Genome Project (MGP) out of Pennsylvania State University.
The MGP was established to sequence and compile genomic information on the woolly mammoth in an attempt to better understand its lifestyle, relatedness to modern ancestors, and possible reasons for its extinction—among other questions. They used hair (specifically the roots) as the main source for isolating DNA because it is often well preserved and rich in DNA even after a long stint in permafrost. Further, the shafts of the hair are resistant to contamination from bacterial DNA that may complicate sequencing effort.
After sequencing, the arduous task of genome assembly provided insight into the mammoths interesting past. First, they found that 99% of the bases sequenced resembled the corresponding part of the elephant genome and, with further phylogenetic analysis (pictured above), the researchers identified that woolly mammoths are more closely related to Indian elephants than to African elephants. By comparing the genetic sequences of Indian elephants and the mammoth, the team could estimate that the evolutionary split occurred around 7 million years ago.1
As for the final extinction of the mammoth, deep sequencing of the mitochondrial genome from a population based on Wrangel Island (the last population) gave integral insight into the disappearance of the species. Comparison with a progenitor population from thousands of years earlier—when Wrangel Island was still connected to mainland Eurasia—revealed a significant decrease in genetic diversity in mammoth populations that predated their final extinction. These results reveal that, at some point around nine thousand years ago, a population of between 149-819 mammoths was isolated by rising sea levels on the island. During the remainder of their existence, no further loss of genetic variation occurred, meaning that their extinction must have occurred rapidly instead of gradually. This data supports the theory that the arrivals of humans in the area led to over-hunting and subsequently a swift extinction.2
With the genome sequenced and questions answered, there has been much speculation in recent years as to whether it is possible to clone a mammoth and whether it would be worthwhile to do so. Should anyone decide to undertake the project, a general plan has been proposed that would include hybridization or genome editing of Indian elephant genomes to introduce specific woolly mammoth DNA. Teams such as the Harvard Woolly Mammoth Revival Team have been looking at using genome-editing technology, like CRISPR, to introduce specific alleles that could help modern elephants adapt to the woolly mammoths native tundra ecosystem.
The promise of this technology raises some hairy ethical questions. For instance, there may have been a good reason that the mammoths died off; possibly, they were not compatible with some element of Holocene life. Is it worth the expense to bring back an animal that died off long ago, only to watch it struggle in an epoch it has not adapted to? Who would be responsible for the safety and study of these valuable creatures? Would genetic manipulation on this scale lead to unencumbered “genome designing� These and many other important questions need to be addressed. Ethical conundrums aside, if completed, this project would represent an unprecedented step forward for conservational efforts and the potential of genetic engineering to revive a number of extinct species.
Patrick Griffin is an undergraduate Genetics major at the University of Georgia. He enjoys cycling, science, and eating donuts, though not necessarily in that order, and once solved a Rubik’s Cube in under a minute. Follow him on Twitter: @patrick_griffN or contact him via email: pgriff10@uga.edu
