A new study published in the journal Nature is describing the extraction and sequencing of the oldest known sample of DNA. The sample comes from an ancient species of mammoth found in the Siberian permafrost and dates back nearly 1.2 million years.
DNA degrades surprisingly fast. Most of the DNA in your body degrades within a few thousand years of you dying. Kept in ideal frozen conditions DNA can last hundreds of thousands of years, although many scientists suggest around one million years is still the upper theoretical limit for DNA survival.
In 2013, a team of Danish scientists made history by sequencing the 700,000-year-old genome of a horse found in the Canadian permafrost. The research was a technical triumph as before this innovative work no full genomic sequence older than 70,000 years had even been characterized.
Now, in an incredibly dazzling achievement an international team of scientists has sequenced full genomic data from three mammoth specimens dating back to the Early and Middle Pleistocene periods. The oldest specimen has been dated at 1.2 million years old.
"This DNA is incredibly old,” notes senior author Love Dalén. “The samples are a thousand times older than Viking remains, and even pre-date the existence of humans and Neanderthals.”
The three mammoth tooth fossils used in the research were uncovered in northeastern Siberia, and DNA sequencing on the oldest specimen revealed a previously unknown genetic lineage of mammoth, rewriting the evolutionary history books. The new lineage is being dubbed the Krestovka mammoth and it is suspected to have diverged from other mammoth lineages around two million years ago.
"This came as a complete surprise to us,” says Tom van der Valk, lead author on the study. “All previous studies have indicated that there was only one species of mammoth in Siberia at that point in time, called the steppe mammoth. But our DNA analyses now show that there were two different genetic lineages, which we here refer to as the Adycha mammoth and the Krestovka mammoth. We can't say for sure yet, but we think these may represent two different species.”
Ancient DNA discoveries have been notoriously controversial in recent years. Despite the general belief that DNA cannot, under any environmental condition, survive much more than a million years, some researchers have suggested there is evidence to the contrary.
Most infamous perhaps is a 2007 claim of finding T-rex tissue and proteins genetically linking the dinosaur to modern ostriches. This finding was subsequently debunked after palaeontologists from the University of Manchester claimed the specimens were contaminated with traces of modern ostrich DNA.
More recently, a controversial study from palaeontologists at the Chinese Academy of Sciences and North Carolina State University claimed to have found organic material in 75-million-year-old dinosaur fossils. That research boldly suggested there may be specific contexts where ancient DNA can survive for tens of millions of years.
Anders Götherström, an author on this new research and professor in molecular archaeology at Stockholm’s Centre for Palaeogenetics, doesn’t suggest DNA can survive for tens of millions of years. However, he does think the traditional million-year limit may be conservative, and it is possible older DNA could be found in certain icy parts of the world.
“One of the big questions now is how far back in time we can go,” asks Götherström. “We haven't reached the limit yet. An educated guess would be that we could recover DNA that is two million years old, and possibly go even as far back as 2.6 million. Before that, there was no permafrost where ancient DNA could have been preserved.”
The new study was published in the journal Nature.
Source: Stockholm University
