Bengaluru: Scientists have managed to sequence the world’s oldest DNA recovered from one of three tooth specimens that belonged to million-year-old mammoths. The specimens came from three different mammoths, and the older two were over a million years old.
The oldest of the three DNAs is dated to be between 1.2 and 1.65 million years old. Another specimen is also over one million years old. Until this discovery, the oldest DNA previously sequenced by humans came from a 560,000-780,000 year-old horse leg bone in 2013.
The oldest molar has been nicknamed the Krestovka mammoth, after the village near which it was discovered, in the Siberian permafrost. The other two are called the Adycha mammoth — dated between 1.1 and 1.3 million years old — and the Chukochya mammoth, dated between 500,000 and 800,000 years old.
The mammoth specimens were excavated in the 1970s. But the DNA samples, which would have rapidly degraded, were preserved well because of the freezing conditions.
The findings were published in the journal Nature this week.
Details of the discovery
The research team was able to obtain 49 million base pairs of nuclear DNA from the Krestovka mammoth, 884 million base pairs from the Adycha sample, and 3.7 billion base pairs from the Chukochya molar.
The DNA sequences revealed new clues to the identity and genetic lineage of the two oldest mammoths, as well as to the one we know as the woolly mammoth (Mammuthus primigenius) that roamed the lands of North America.
The two oldest mammoths pre-dated the woolly mammoth, that became extinct about 4,000 years ago on a remote island where an isolated population had survived. The researchers found that the Adycha specimen was a steppe mammoth (Mammuthus trogontherii), the only species known to have inhabited Siberia.
But the Krestovka specimen, the oldest one, seems to have belonged to a completely new lineage of steppe mammoths. They had diverged from other steppe mammoths and are likely a new species.
The researchers also found evidence of inter-breeding between these different lineages. For example, they found that Columbian mammoths (Mammuthus columbi), also a North American species, descended from both the woolly mammoth and the Krestovka lineage.
The scientists think they now have an explanation about why all sequenced Columbian mammoths sequenced so far had mitochondrial genomes — genetic information entirely inherited from an animal’s mother — closely related to those of woolly mammoths. It was because the Columbian mammoths too mated with female woolly mammoths.
Significance of the discovery
Scientists have long waited to discover DNA that is over one million years old. The latest discoveries are the first ones dated over one million years old.
The latest discovery is also the first genetic evidence from ancient DNA of ‘hybrid speciation’, an evolutionary biology theory which states that a new species can also form by the mixing of two different species, instead of simply by splitting from a parent species.
While it is unclear when adaptations for colder climates such as woolly fur and increased fat deposits started to appear in the mammoth evolutionary tree, the scientists were able to confirm that these animals had these adaptations one million years ago.
The Krestovka DNA, the oldest DNA extracted, also leads to the possibility of excavating even older remains as the Siberian permafrost continues to thaw at an alarming rate due to global heating.
The oldest human relative (‘hominin’) that has been confirmed with DNA, an early Neanderthal in a Spanish cave, dates to about 430,000 years ago. Scientists have speculated that under the right setting, million-year-old remains of ancient human relatives and ancestors could also be found.
The age limit of these discoveries is 2.6 million years, which is the age of the permafrost. The conditions before that would have been too warm to have helped preserve ancient DNA, the scientists have clarified.
Although Krestovka DNA is the oldest DNA that has been extracted, other older organic material and bio molecules have been discovered before. In 2016, scientists had extracted the oldest ever protein from 3.8 million-year-old ostrich eggshells in Tanzania.