WASHINGTON – Scientists have recovered the oldest recorded DNA and extracted it from the mammoth molars that roamed northeastern Siberia until 1.2 million years ago in research that broadens the horizons to understand extinct species .
Investigators said Wednesday they had recovered and sequenced DNA from the remains of three individual mammoths – cousins of elephants that were among the large mammals that dominated ice age landscapes – buried in permafrost conditions leading to the preservation of ancient genetic material.
Although the remains were discovered from the 1970s onwards, new scientific methods were needed to extract the DNA.
The oldest of the three, discovered near the Krestovka River, was about 1.2 million years old. Another, near the Adycha River, was approximately 1 to 1.2 million years old. The third, coming from near the Chukochya River, was about 700,000 years old.
“This is, by a wide margin, the oldest DNA ever recovered,” said evolutionary geneticist Love Dalén of the Swedish Center for Paleogenetics, who led the research published in the journal Nature.
Until now, the oldest DNA came from a horse that lived in the Canadian territory of the Yukon about 700,000 years ago. By comparison, our species, Homo sapiens, first appeared about 300,000 years ago.
DNA is the self-replicating material that carries genetic information in living organisms, a kind of life plan.
“This DNA was extremely degraded into very small pieces, and so we had to sequence many billions of ultra-short DNA sequences in order to baffle those genomes,” Dalén said.
Most knowledge about prehistoric creatures comes from the study of skeletal fossils, but there is a limit to what these can explain about an organism, especially in relation to relationships and genetic traits.
Old DNA can help fill in the blanks, but it is highly perishable. New sophisticated research techniques allow scientists to recover increasingly old DNA.
“It would be a wild conjecture, but it should be done for a maximum of two to three million years,” Dalén said.
This could shed light on some past species, but would leave many others unattainable, including dinosaurs, which became extinct 66 million years ago.
“When we can obtain DNA on a scale of millions of years, we can study the process of speciation (formation of new species) in a much more detailed way. Morphological analyzes on bones and teeth often allow researchers to study a handful of fossil features, while with genomics we are analyzing many tens of thousands of features, ”Dalén said.
The researchers gained insights into the evolution and migration of mammoths by comparing DNA with that of the most recently lived mammoths. The last mammoths disappeared about 4,000 years ago.
The oldest of the three specimens, the Krestovka mammoth, belonged to a hitherto unknown genetic lineage that more than 2 million years ago deviated from the lineage that led to the well-known woolly mammoth.
SciLifeLab geneticist Tom van der Valk in Sweden, the first author of the study, said it appears that members of the Krestovka lineage were the first mammoths to migrate from Siberia to North America by a land bridge that disappeared about 1.5 million years ago mammoths later migrated about 400,000 to 500,000 years ago.
The lineage of the Adycha mammoth was apparently ancestral to the woolly mammoth, they found, and the individual Chukochya is one of the earliest specimens of the woolly mammoth known.
DNA analyzes showed that genetic variants associated with enduring icy climates such as hair growth, thermoregulation, fat deposits, cold tolerance, and circadian rhythms were present long before the origin of the woolly mammoth.