A rich and complex ecosystem stretching back 700,000 years that included woolly mammoths, bison, horses and big cats has been unveiled thanks to DNA preserved in frozen faeces.

(±«°ů´Çł¦ľ±łŮ±đ±ô±ôłÜ˛őĚý±č˛ą°ů°ů˛âľ±ľ±) are rodents about 40 centimetres long, found in cold regions of both North America and Siberia. These areas were joined by a land bridge in the past, with the whole region being known as Beringia.

“The squirrels hibernate for about eight months of the year, and in the four months that they’re conscious, they really need to get out there and eat and bring as many resources as they can back to their burrow,” says at the Hakai Institute in Campbell River, Canada.

This means their burrows often contain a wealth of faecal pellets and food caches, which makes the animals like “natural archivists”, says Murchie. To see what might be stored in this archive, he and his colleagues looked at preserved faeces – known as coprolites – from 13 Arctic ground squirrel burrows in the central Yukon in Canada that were frozen in permafrost.

The burrows dated to between about 700,000 and 30,000 years ago. From the droppings, each of which is about 1 to 2 centimetres long, the team extracted DNA belonging to a wide range of organisms.

These include microbes, more than 200 different plant groups and animals including insects, other rodents, woolly mammoths, horses, grey wolves, steppe bison and a big cat that was either an or a cougar. “It’s the whole cast of organisms that lived in the Beringian ice-age ecosystem,” says Murchie.

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You might assume that ground squirrels would primarily eat nuts and seeds, but that’s not the case, he says. “They’re actually quite omnivorous, almost like little bears. There are reports of ground squirrels eating carcasses of moose and lynx, so the fact that we find all of these large animals in their coprolites isn’t actually that surprising.”

Murchie and his colleagues were able to use the DNA they found to reconstruct mitochondrial genomes of many animals from different points in time. These included 12 ground squirrels – one lineage of which dated back 700,000 years – three horses, two bison and one hare. They also found enough DNA to piece together six woolly mammoth genomes, but details of those will be published separately.

“These are fantastically preserved samples that really showcase the ecological diversity of the Yukon through time,” says at Clemson University in South Carolina.

She says it is hard to know whether DNA from a given species is present in a coprolite because it was eaten by a ground squirrel, or because it existed in the environment and leached in. But she does say it is feasible that the rodents consumed mammoth meat, given how much DNA was present in the samples and that ground squirrels are often scavengers.

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James Watson, one of the discoverers of the structure of DNA, has died in a New York hospice facility at the age of 97. Along with fellow researchers Francis Crick and Maurice Wilkins, he won the 1962 Nobel Prize in Physiology or Medicine for the discovery of DNA’s double helix shape, which laid the groundwork for innumerable innovations throughout the field of biology.

After that revolutionary discovery, Watson went on to serve as the director, president and chancellor of Cold Spring Harbor Laboratory in New York. Under his direction, the laboratory expanded significantly, becoming a world leader in molecular biology. He was also the head of the Human Genome Project for two years before stepping down in protest of moves towards patenting gene sequences.

Despite all this, Watson told 91av in 2007 that he viewed the books he authored as his biggest accomplishment, saying: “The double helix was going to be found by someone. I speeded it up a little. But Francis Crick never would have written The Double Helix, nor would any of the other scientists involved.” Watson said at the time that he hoped his writing would encourage more young people to go into science.

He faced a great deal of controversy throughout his career. The very discovery of the structure of DNA was enabled by X-ray images taken by another researcher, Rosalind Franklin, whose work was not acknowledged in the 1953 paper that won Watson and Crick their Nobel prize, and Watson was criticised for downplaying her contributions. He was famously dismissive of other fields of biology, and frequently faced condemnation and even professional censure for comments about both other researchers and marginalised groups in general, which by 2007 led to his retirement from Cold Spring Harbor.

Despite his many controversies, his academic accomplishments place him as one of the most important scientists of the 20th century. His work opened the door to entirely new fields of study, bringing us insights on how hereditary information is stored, the relationships between species across the tree of life and new ways to treat genetic diseases.

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