Feb. 17 (UPI) -- The world's oldest DNA, recovered from 1.2-million-year-old mammoth teeth, has offered scientists new insights into the genomic history of mammoths.
Scientists recovered and sequenced DNA from the teeth of three mammoth specimens preserved in the permafrost of eastern Siberia.
Using the latest genomic sequencing technologies, including new methods for distinguishing between mammoth DNA and contaminating DNA from bacteria and humans, researchers were able to sequence the genomes of the the specimens.
The sequencing work, described Wednesday in the journal Nature, showed one of the three mammoths was not like the other two.
"Two of the specimens belonged to the same genetic lineage, which initially comprised a type of steppe mammoth that later evolved into the woolly mammoth," senior author Love Dalén told UPI in an email.
"The third specimen, Krestovka, belonged to a previously unknown genetic lineage of mammoth, which we think was the same lineage that colonized North America more than 1 million years ago," said Dalén, a professor evolutionary genetics at the Center for Paleogenetics in Stockholm, Sweden.
Scientists used both molecular clock data and geologic data to date the three mammoths, yielding a more detailed evolutionary history.
The collection of geologic data involved both biostratigraphy -- the dating of other animals in the icy layers from which the mammoth remains were recovered -- and paleomagnetism, which involves the use of Earth's magnetic pole reversals as dating benchmarks.
"The molecular clock dating makes use of mutations that happen at a relatively constant rate through time, and that this clock rate can be calibrated, for example, by comparing multiple much younger but radiocarbon dated specimens, and through the known divergence time between mammoths and elephants," Dalén said.
The molecular clock data showed the steppe-turned-wooly mammoth lineage shared a common ancestor with the newly discovered lineage, dubbed the Adycha lineage, more than 2 million years ago.
The genomic analysis showed that the Columbian mammoths that populated North America belonged to a hybrid lineage. The joining of the Adycha mammoth and the Krestovka mammoth lineages, researchers determined, occurred roughly 420,000 years ago.
Researchers were also able to confirm that the genetic variants that helped the wooly mammoth survive frigid Arctic conditions emerged early in the mammoth's evolutionary history.
The ancient DNA of the Adycha mammoths revealed the gene variants responsible for hair growth, thermoregulation, fat deposits, cold tolerance and circadian rhythms.
The findings suggests vital genetic adaptations don't arrive all at once, but instead emerge slowly over time, the researchers said.