For millions of years, mammoths roamed Europe, Asia and North America. Around 15,000 years ago, these giant animals began to disappear from their vast range and now only survive on a few islands.
Eventually, mammoths disappeared from these reserves as well, with the exception of Wrangel Island, a Delaware-sized island more than 80 miles north of the Siberian coast, where mammoths survived for thousands of years and were still alive when the Great Pyramids were built in Egypt.
When the Wrangel Island mammoths disappeared 4,000 years ago, mammoths became extinct forever.
Geneticist Lav Dalen of Stockholm University and his colleagues have been extracting DNA from fossils on Wrangel Island for 20 years, and in recent years collected the entire genome of the mammoth. On Thursday, they published their reconstruction of the enigmatic animal's genetic history.
Scientists concluded that the island's mammoth herd began as a small group of fewer than 10 animals about 10,000 years ago. The herd survived for 6,000 years, but the mammoths were plagued by a number of genetic diseases.
Oliver Ryder, director of conservation genetics at the San Diego Zoo Wildlife Alliance, said the study contains important lessons for trying to save species from extinction today: It shows that inbreeding can cause long-term harm.
“Studying mammoths allows us to look at that process over thousands of years,” said Ryder, who was not involved in the research. “We don't have that data for the species we're trying to save today.”
Dr. Dalen and his colleagues looked at the genomes of 14 mammoths that lived on Wrangel Island between 9,210 and 4,333 years ago. The researchers compared the DNA of the Wrangel Island mammoths with the genomes of seven mammoths that lived on the Siberian mainland up until 12,158 years ago.
Every animal's genome contains a wealth of information about the population it came from. Large populations lead to high genetic diversity, meaning animals inherit many different versions of genes from their parents. Small populations lead to animals inbreeding, meaning they inherit many identical copies of genes.
Wrangel Island's oldest fossils contain identical versions of many genes, leading Dr Dalen and his colleagues to conclude that the island was founded by a surprisingly small population of mammoths.
Until about 10,000 years ago, Wrangel Island was a mountainous region of mainland Siberia. Few mammoths spent time there, preferring lower elevations where vegetation was more abundant.
But at the end of the Ice Age, the glaciers melted and flooded the northern tip of Siberia. “When Wrangel Island became separated from the mainland, it just so happened that there was a herd of little mammoths on it,” Dr Dalen said.
Mainland mammoths faced great challenges to survival: humans hunted them, and climate change caused much of their grassland habitat to disappear, replaced by tundra.
However, the few mammoths stranded on Wrangel Island were extremely lucky: the island was free of humans and other predators, and there was no competition from other herbivores. Moreover, Wrangel Island's climate provided an ecological time capsule where the mammoths could still enjoy the diversity of Ice Age plants.
“Wrangel Island was a great place to live,” Dr. Darren said.
He and his colleagues found that Wrangel Island's mammoth population grew from fewer than 10 to about 200, likely the maximum number of mammoths that the island's vegetation could support.
But life for the Wrangel mammoths was far from perfect: the few animals that made up the island had very little genetic diversity, and Dr Dalen and his colleagues found that levels remained low for the next 6,000 years.
“They're carrying over the inbreeding they suffered in the early years,” he said.
As a result, the mammoths were likely suffering from hereditary diseases. Dr. Dalen believes that these diseased mammoths were able to survive for hundreds of generations because they had no predators or competition. The Wrangel Island mammoth herd would probably have disappeared quickly from the mainland.
The new study doesn't explain how the Wrangel Island mammoths became extinct — there's no evidence that humans were the cause — but the earliest known visitors to Wrangel Island likely set up a summer hunting camp there 400 years after the mammoths went extinct.
For now, Dr Darren can only speculate about the true cause of the mammoths' extinction – the war in Ukraine has prevented him and his colleagues from traveling to Russia to carry out further research.
The Wrangel Island mammoths could have been wiped out by a tundra fire or an Arctic volcanic eruption, and Dr Dalen said it's possible that migratory birds brought the influenza virus to Wrangel Island, which infected the mammoths and caused their extinction.
“There are many possible explanations but we haven't been able to narrow it down yet,” he said.
Dr Dallen believes the new research bodes ill for conservation biologists trying to save endangered species, as even if they increase a species' population, they may still suffer from low genetic diversity.
Dr Darren said it may be essential to increase the genetic diversity of recovering populations, and conservation biologists are researching ways to achieve this, such as moving animals between populations so they can interbreed.
Cloning could be another way to help revive species. Dr. Ryder and his colleagues have been freezing cells from endangered animals to preserve some of their genetic diversity. In 2021, researchers successfully cloned a black-footed ferret from a population that went extinct in the 1980s.
Without such interventions, endangered species may struggle to escape the legacy of inbreeding even after hundreds of generations: “There may still be time bombs ticking in their genomes that are not good for the long term,” Dr Ryder said.