A new record in the field of ancient DNA has been achieved! A million-year-old DNA has been extracted and sequenced! The source of DNA was mammoth teeth found in the eastern Siberian permafrost which was sufficiently good to produce the oldest ancient DNA on record. The DNA was extracted from the three-tooth specimens excavated back in the 1970s. The study has been published in Nature under the title Million-year-old DNA sheds light on the genomic history of mammoths.
Researchers consider this as a symbolic breakthrough in the field of ancient DNA which in a way started with the draft publication of the Neanderthal genome (article) back in 2010. With sequencing the Neanderthal genome started a super-fast development of this fields with hundreds of ancient genomes being sequenced in the last 10 years. Up to now the oldest ancient DNA being extracted and sequenced was from the horse leg bone being between 560,000 and 780,000 years old (article) and among humans, the oldest recovered ancient DNA was from the Neanderthal genome being ~430,000 years old. It had been suspected that ancient DNA could survive beyond one million years if the right samples could be found. DNA starts with degradation once an organism dies, this process starts with chromosomes being broken into pieces that get shorter over time. Ultimately, these DNA pieces become so small that even if they are extracted it is hard to retrieve DNA information. However, the cold environment of permafrost from which the mammoth samples have been extracted slowed down the process of DNA degradation.
What Did We Learn From The Million-Year-Old Genome?
Besides the technical achievement of extracting and sequencing the million-year-old DNA, there are new scientific insights retrieved from these genomes.
The main message from this study is that there were two distinct mammoth lineages in eastern Siberia at the time, where one of the lineages gave rise to the woolly mammoth (Mammuthus primigenius) and the other represents a previously unrecognized lineage that was ancestral to the first mammoth that inhabited North America.
The analysis reported in this study shows that the Columbian mammoth of North America has its ancestry to a Middle Pleistocene hybridization between the woolly mammoth and this previously unrecognized lineage with roughly equal admixture proportions.
Finally, the study showed that the majority of protein-coding changes associated with cold adaptation in woolly mammoths were already present one million years ago. These findings highlight the potential of deep-time palaeogenomics to expand our understanding of speciation and long-term adaptive evolution.
This study is also the first one that reports hybrid speciation from ancient DNA. Hybrid speciation refers to the type of speciation (speciation: an evolutionary process by which a new population develops to become a new species) where hybridization between two different species leads to a new species which is reproductively isolated from the parent species.
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