For millions of years, mammoths inhabited Europe, Asia and North America. About 15,000 years ago, the giant animals began disappearing from their vast range, surviving only on a few islands.
Eventually, they disappeared from these refuges as well, with one exception: Wrangel Island, a land mass the size of Delaware more than 80 miles north of the coast of Siberia. There, mammoths held out for thousands of years: they were still alive when the great pyramids were built in Egypt.
When the mammoths of Wrangel Island disappeared 4,000 years ago, the mammoths disappeared for good.
For two decades, Love Dalén, a geneticist at Stockholm University, and his colleagues have been extracting pieces of DNA from fossils on Wrangel Island. In recent years, they have collected entire mammoth genomes. On Thursday, they published a reconstruction of the genetic history of these enigmatic animals.
Scientists concluded that the island’s population was founded around 10,000 years ago by a small herd of fewer than 10 animals. The colony survived 6,000 years, but the mammoths suffered from many 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. This shows that inbreeding could cause long-term damage.
“This massive study allows us to look at this process over thousands of years,” said Dr. Ryder, who was not involved in the new study. “We don’t have data like this for the species we are currently trying to save.”
Dr. Dalén and his colleagues examined the genomes of 14 mammoths that lived on Wrangel Island between 9,210 and 4,333 years ago. The researchers compared the DNA of mammoths from Wrangel Island with seven genomes of mammoths that lived on the Siberian continent 12,158 years ago.
The genome of any animal contains a huge amount of information about the population to which it belongs. In large populations, there is great genetic diversity. As a result, an animal will inherit different versions of many of its genes from its parents. In a small population, animals will become inbred and inherit identical copies of many genes.
The oldest fossils from Wrangel Island contain identical versions of many genes. Dr. Dalen and his colleagues concluded that the island was founded by a remarkably small population of mammoths.
About 10,000 years ago, Wrangel Island was a mountainous region located on the Siberian continent. Few mammoths stayed there, preferring lower regions where more abundant plants grew.
But at the end of the Ice Age, melting glaciers submerged the northern edge of Siberia. “There was a small herd of mammoths on Wrangel Island when it was cut off from the mainland,” Dr Dalén said.
The continent’s mammoths faced significant challenges to their survival. Humans have hunted them down, while climate change has destroyed much of their grassland habitat, turning it into tundra.
But the few mammoths stranded on Wrangel Island were extremely lucky. The island was free of people and other predators, and they faced no competition from other grazing mammals. Additionally, Wrangel Island’s climate made it an ecological time capsule, where mammoths could still enjoy a diversity of Ice Age plants.
“Wrangel Island was a golden place to live,” Dr. Dalén said.
He and his colleagues found that the population of Wrangel Island had increased from fewer than 10 mammoths to around 200. This was probably the maximum number of mammoths that the island’s flora could support.
But life was far from perfect for the Wrangel mammoths. The few animals that founded the island had very little genetic diversity, and Dr. Dalén and his colleagues found that this level remained low for the next 6,000 years.
“They took with them the inbreeding that they acquired early on,” he said.
As a result, mammoths likely suffered from a high level of hereditary diseases. Dr. Dalén suspects that these diseased mammoths managed to survive for hundreds of generations because they had no predators or competitors. The Wrangel Island herd would probably have quickly disappeared from the mainland.
The new study doesn’t reveal exactly how Wrangel’s mammoths perished. There is no evidence that humans are responsible; the first known visitors to Wrangel Island appear to have established a summer hunting camp 400 years after the mammoths became extinct.
For now, Dr. Dalén can only speculate about the true cause of the gigantic extinction. The war in Ukraine made it impossible for him and his colleagues to travel to Russia to further their research.
It is possible that a tundra fire killed the Wrangel mammoths, or that the eruption of an Arctic volcano destroyed them. Dr. Dalén can even imagine that a migratory bird brought a flu virus to Wrangel Island, which then jumped to the mammoths. and annihilated them.
“We’re still left with a number of possible explanations, and we still haven’t been able to narrow them down,” he said.
Dr. Dalén thinks the new study bodes ill for conservation biologists trying to save species near extinction. Even if they restore a species to a larger population, it may still face a low level of genetic diversity.
Dr Dalén said boosting the genetic diversity of recovering populations could be key. Conservation biologists have studied how to do this, such as moving individual animals between populations so they can interbreed.
Cloning could be another way to contribute to species recovery. Dr. Ryder and his colleagues froze cells from endangered animals to preserve some of their genetic diversity. In 2021, researchers successfully produced a black-footed ferret clone from a population that went extinct in the 1980s.
Without these interventions, an endangered species might struggle to escape a legacy of inbreeding, even after hundreds of generations. “There may still be ticking time bombs in its genome that don’t bode well in the long term,” Dr Ryder said.