The first woolly mammoths were warm, but the last woolly mammoths were warmer. In fact, published article in Current Biology states that the woolly mammoths’ best-known traits, including their fluffy fur, have intensified throughout their 700,000-year stay in Siberia.
Lub Dahlen, one of the authors of the article, poses with the mammoth Yuka, whose genome was included in the analyses. (Credit: Ian Watts)
Woolly, Woolly, Woollier
The woolly mammoth’s iconic feature, its fur, has allowed the species to survive and thrive on the cold steppes of Siberia for more than 700,000 years. But despite its importance to the species, experts have always wondered about the trait, struggling to determine when it developed and how it transformed over time.
Trying to solve these shaggy mysteries, a team of paleontologists and paleogeneticists sequenced the genomes of 23 woolly mammoth specimens and studied their similarities and differences. “We wanted to know what makes a mammoth a woolly mammoth,” said David Diez-del-Molino, a specialist on the team and at the Center for Paleogenetics in Stockholm, Sweden, according to press release.
While other teams have compared one or two woolly mammoth genomes in the past, the team chose to compare an abundance of genomes at once. This allowed the specialists to identify which mutations were widespread and which were not widespread among mammoths in Siberia, revealing which mutations were adaptive and which were not.
Ultimately, the results revealed that mammoth wool was present from the beginning of the species, but became more prominent over time, making the mammoth better suited to its frigid environment.
Read more: Millions of years of DNA yield huge surprises
A braid of mammoth features
The team sequenced the genomes of 23 woolly mammoths, 16 of which had never been sequenced before. They wanted to identify genes that had been present among mammoths for a long time and had accumulated many mutations during that time. While one of the preserved specimens, Chukochialived about 700,000 years ago and is one of the oldest in the world, the other 22 specimens lived about 100,000 years ago or less.
“Having the Chukochya genome allowed us to identify a number of genes that evolved during the woolly mammoth’s lifetime as a species,” said Lav Dahlen, another specialist on the team and a professor at the Center for Paleogenetics, according to the release. “This allows us to study evolution in real time and we can say that these specific mutations are unique to woolly mammoths and did not exist in its ancestors.”
Overall, the 700,000-year-old genome shares almost 92 percent of its mutations with the 100,000-year-old genomes, suggesting that many of the woolly mammoth’s traits were already present when the species split from its ancestor, the steppe mammoth.
That being said, these traits have evolved throughout the woolly mammoth’s existence. “The earliest woolly mammoths were not fully evolved,” Dahlen said, according to the release. “Their wool was different—perhaps less insulating and fluffy compared to later woolly mammoths.”
Not surprisingly, the majority of genes that were shared between mammoths were related to the cold conditions of their climate. For example, the genomes of these specimens show an advanced ability to metabolize and store fat and to sense temperatures that only increase with time.
The team also compared the mammoth genomes to the genomes of more modern species, including those of Asian and African elephants. They found, to their surprise, that several of the mammoth mutations are still found today, but not in elephants, but in animals that are adapted to the Arctic.
“We found some highly evolved genes related to fat metabolism and storage that are also found in other Arctic species such as reindeer and polar bears, meaning that there is likely convergent evolution for these genes in cold-adapted mammals,” says DÃez-del-Molino, according to the publication.
Of course, modern mammoths also demonstrated several mutations not shared by ancient mammoths, including mutations in their immune systems. These mutations may have provided the 100,000-year-old mammoths with enhanced immunity against viral pathogens.
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