Prehistoric DNA sequencing: Jurassic Park was not so wide of the mark

Mapping the genome of a horse from 700,000 years ago goes far beyond what was thought possible with DNA sequencing

dna przewalski horse

Strong genes: scientists have sequenced the DNA of a horse that lived 700,000 years ago – far beyond what was thought possible. Photograph: Tierfotoagentur/ Alamy

It remains one of the most intriguing premises for a science fiction film. Near the beginning of Steven Spielberg’s classic Jurassic Park, scientists reveal how they have collected the DNA of dinosaurs from mosquitoes trapped in amber more than 65m years ago. These insects had previously fed on dinosaurs’ blood and by extracting these blood cells, and removing their DNA, entrepreneur John Hammond (Richard Attenborough) recreates genomes of velociraptors, triceratops, and other dinosaurs. From these genomes, he clones the terrifying creatures that go on to terrorise the film’s characters.

At the time, the idea – originally outlined by Michael Crichton in his book Jurassic Park – sounded plausible until researchers pointed out that DNA simply cannot exist intact for such lengths of time. In fact, you would be lucky if you could go back more than a few thousand years before DNA becomes hopelessly fragmented, it was argued. Defences that repair DNA in living cells disappear after death. As a result, DNA strands quickly break up. Hence researchers’ limit of a few thousand years for the feasibility of creating an extinct creature’s genome.

But reality has a way of catching up on science fiction. Technical developments in DNA recovery have slowly transformed the business of recovering ancient genetic material. As a result, in 2010, a team led by Svante Pääbo, at the Max Planck Institute for Evolutionary Anthropology in Germany, revealed it had sequenced the entire genome of a Neanderthal based on three specimens at least 38,000 years old from Vindija Cave, Croatia. The work has since provided critical insights into modern humans’ genetic relationships with this ancient hominin species.

Since then Pääbo’s researchers have pushed their genome sequencing power even further into the past and last year announced they had sequenced the genome of a girl belonging to a species of humans called the Denisovans – a close relation to the Neanderthals – who lived about 80,000 years ago. The study showed she had brown eyes, hair and skin.

But now scientists have taken that sequencing age limit even further – and by a considerable margin. In Nature this week, a team led by Ludovic Orlando of Copenhagen University published a paper in which they reveal the entire genetic sequence of a species of horse that lived around 700,000 years ago – almost 10 times the current limit. It is an extraordinary achievement, one that immediately raises the prospect that scientists might soon create the genomes of creatures that died more than a million years ago, possibly several million years. By that reckoning, Crichton and Spielberg would not seem to be so far out.

Of course, Orlando and his colleagues were fortunate in one respect. Their horse genome was recreated from a bone fragment that was found in the Arctic permafrost at Thistle Creek, Canada. Its DNA had, in effect, been kept in cold storage for all that time. Nevertheless, unravelling it involved the use of advanced computing techniques, infomatics, and the ability to study the structures of proteins found in the sample. As Orlando stated: “We were amazed about the quality of the sample. We not only beat the record for [oldest] genome characterisation by almost an order of magnitude… we also discovered that a whole bunch of approaches can be used to characterize the deep evolutionary past.”