Some of the secrets of evolution could be found in the molar teeth of three mammoths that roamed northeastern Siberia — two of them more than a million years ago.
A research team on Wednesday published a study in the journal Nature detailing the successful collection of DNA from fossilized mammoths, making it by far the oldest genetic material ever studied.
And its age is only part of its importance. Scientists said they can compare the DNA samples to reveal how the genetics of an earlier species changed as it evolved into a later species, also known as speciation.
“This is the first time that anyone has ever sampled before and after a speciation event, to trace the genomic changes that happen during speciation,” said Love Dalén, a professor in evolutionary genetics at the Centre for Palaeogenetics in Stockholm and an author of the study.
The oldest “ancient DNA” previously recovered was from the remains of a Siberian horse about half as old as the mammoths.
The study describes research on the fossils of three mammoths unearthed in the 1970s by Russian paleontologists. They’ve since been kept in archaeological collections, and the new study used DNA extracted from their molar teeth, Dalén said.
One crucial factor in the work was that the fossils were surrounded by permafrost – a layer of subsoil in polar regions that stays frozen throughout the year. DNA degrades rapidly when it is exposed to liquid water, and so the frozen soil was pivotal to recovering such ancient genetic material, he said.
The researchers have dubbed the oldest mammoth fossil “Krestovka,” and say the age of the permafrost layer where it was found suggests it is about 1.65 million years old.
Another fossil,“Adycha,” dates from about 1.34 million years ago, while the third,“Chukochya,” dates from about 870,000 years ago. The three names come from rivers in Siberia.
The genetics of all three mammoths, revealed in the sequences of millions of genes produced from their ancient DNA, show there were two distinct lineages of what are called “steppe mammoths” (Mammathus trogontherii) in Siberia about a million years ago, although only one lineage was known about, Dalén said.
Adycha and Chukochya came from the line that gave rise about 700,000 years ago to the woolly mammoth species (Mammathus primigenius), but Krestovka belonged to the previously unrecognized lineage.
Examinations of its genetic material suggested that the Krestovka lineage diverged from other mammoths 1.78 million to 2.66 million years ago, and that it was ancestral to the first mammoths to colonize North America, he said.
Some scientists claimed in the 1990s that they had recovered genetic material from fossilized dinosaur eggs dated to more than 140 million years ago, but those studies used a method of DNA analysis called PCR – polymerase chain reaction – which has been found inadequate, Dalén said.
The latest study used a more accurate method called “shotgun sequencing,” which reproduces distinctive damage in parts of the DNA genome that shows it is authentically ancient, he said.
The recovery of such ancient DNA raises the possibility it could be used to “resurrect” extinct mammoths, perhaps by modifying the genetics of an elephant fetus – elephants and mammoths shared a common ancient ancestor about 6 million years ago.
But Dalén said he is skeptical that such an idea could work, because comparatively little of the entire genome of extinct mammoths can be recovered in ancient DNA samples.
The prospects for using ancient DNA techniques for studying human evolution may be slightly better.
Paleontologists have found numerous fossils of our ancestral species, some dating back millions of years, but only in warm regions where their DNA is not preserved by permafrost, Dalén said.
However, there remains a possibility that fossils of ancestral human species might someday be found frozen in the permafrost of the far north, and these techniques could be used on them, he said.
Alfred Roca, a geneticist and professor of animal sciences at the University of Illinois Urbana-Champaign, said the study means biologists can now use ancient DNA to study genetic changes as extinct species diverged from each other: “You don’t have to infer things, you don’t have to use some sort of deductive method; you can actually see the DNA.”
Roca, who researches the genetics of modern elephants, was not involved in the latest study but reviewed it for Nature.
He said one future step might be to use the new ancient DNA techniques on the fossils of other animals preserved in the permafrost, especially small rodents such as pikas, voles and lemmings.
“Genomics has been pushed into deep time by the giants of the Ice Age — the wee mammals that surrounded them might soon also have their day,” Roca wrote.