Solving evolutionary puzzles
By David Smith
Sometimes explorers find great treasures buried in the snow. The comic book adventurer Tintin, for instance, would often stumble upon large stores of precious jewels and gems beneath Arctic sea ice. But some of the most important and exciting finds are arguably the remains of ancient creatures frozen in time. Mammoths, giant bears, sabre-toothed cats, nine-ft beavers, 20-ft sloths, prehistoric buffalo, Arctic horses, early migrating humans, all of these and more have been recovered from polar regions. These biological puzzle pieces, in addition to being the ultimate museum specimens, are crucial for understanding biodiversity and evolution.
Unearthing a magnificent beast from ice, snow, or permafrost is a rare and remarkable event. It gives researchers a window into another era. But, until recently, the view through that window has been relatively narrow — limited to comparative studies of things like bone and body structure and stomach content. Today, however, with the advent of new technologies, researchers are able to obtain unprecedented amounts of information from these age-old carcasses, and use it to unravel the origin and history of life on Earth.
Major advances in genetic sequencing techniques have made it fast, easy, and cheap to sequence huge quantities of DNA from just about any unspoiled cell or tissue of an organism. The beauty about species trapped within ice and snow is that they can be very well preserved, allowing scientists to isolate intact DNA from their cells for sequencing. In particularly with old samples, where little or no soft tissue remains, researchers have to dig deep into the bone or fossil to find quality DNA. This is precisely how an international team of scientists, including members from the University of Alberta, sequenced the genome of an approximately 700,000-year-old Arctic horse,
which once roamed the dry, grassy tundra.
About 10 years ago in an old Yukon mine south of Dawson City, Canadian researchers struck gold when they discovered the fossilized bone of an ancient horse within the permafrost. Luckily, the frozen soils had preserved enough of the horse’s DNA to allow the scientists to piece together its genome. The results, which were published last summer in the journal Nature, allowed the scientists to understand the relationships among different horse lineages, including the Mongolian Przewalski’s horse — the only remaining group of wild horses. The research team calculated that the last common ancestor of zebras, donkeys, and present-day horses, including the Przewalski’s horse, lived about four to 4.5-million years ago, which is twice as old as previously believed. The study was also a remarkable feat for genetics as it represents the oldest genome ever sequenced, and provides a glimpse of what is to come from future studies. It likely won’t be long until scientists are digging up fossils and pumping out genomes on a regular basis.
In fact, shortly after the publication of the horse genome, a group of mainly European biologists sequenced DNA from the bone of a 300,000-year-old cave bear excavated from a site in the Atapuerca Mountains in Spain. Although the cave bear sample is not nearly as old as the Yukon horse fossil, the accomplishment of sequencing some of its DNA was made more impressive by the fact that the bear was not collected from ice or snow. This, as the authors write in the Proceedings of the National Academy of Sciences, “demonstrates that DNA can survive for hundreds of thousands of years outside of permafrost and opens the prospect of making more samples from this time period accessible to genetic studies.”
Recently, the genes from an ancient polar bear may have helped solve an enduring and controversial mystery: does the Yeti or “Abominable Snowman” exist? And if yes, what is it? It all began when renowned Oxford biologist and genome guru Bryan Sykes got his hands on two supposed samples of Yeti hair — one collected in the mountains of northern India by a French mountaineer 40 years ago and another found in Bhutan about a decade ago. Professor Sykes and his colleagues sequenced genes from the two Yeti samples and then compared them to a massive DNA database to search for similarities to other known species. The results of their analyses are profound: the Yeti — wait for it — might be a big old bear. Indeed, the genes from the supposed Yeti hairs were very similar to those sequenced from the jawbone of an approximately 100,000-year-old polar bear found in the Norwegian Arctic in 2004. Sykes, who described some of his findings in the TV documentary Bigfoot Files, which aired on the National Geographic Channel last November, believes that the Yeti hairs may belong to an unidentified bear species presently living in the Himalayas.
Far from the Himalayas, at the Hermitage Museum in St. Petersburg, Russia, sits the 24,000-year-old skeleton of a four-year-old boy. Archaeologists discovered the young lad’s remains almost a century ago at an Upper Palaeolithic burial ground in south central Siberia, close to Lake Baikal, and this past year researchers used state-of-the-art techniques to assemble the boy’s genome. It’s the oldest genome ever sequenced from a modern human, and has provided a new take on the ancestry of First Nations in North America, whose relatives travelled to the New World from Siberia in the last Ice Age. Some regions of the youth’s genome showed similarities to the genes of western Eurasians whereas other parts were similar to those of First Nations people. This research, described in the journal Nature (2013), suggests that First Nation’s genetic history is more complex than formerly thought, coming from a mixture of different sources, including an ancient population that is related to current day Europeans. We’ll likely learn a lot more about human ancestry and migration as more Palaeolithic human remains are recovered from hidden graves and frozen soils.
You never know what you might find beneath your boots — maybe the world’s oldest elk specimen, just waiting to have its DNA deciphered.
David Smith is an assistant professor in the biology department at Western University.