For millions of years, mammoths roamed Europe, Asia and North America. About 15,000 years ago, these giant animals began to disappear from their vast range until they survived on only a few islands.
Over time, they, too, disappeared from those refuges, with one exception: Wrangel Island, a landmass the size of Delaware more than 80 miles north of the Siberian coast. There, the mammoths resisted 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 became extinct forever.
For two decades, Love Dalén, a geneticist at Stockholm University, and her colleagues have been extracting DNA fragments from fossils on Wrangel Island. In recent years, they have assembled complete 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 about 10,000 years ago by a small herd made up of less than 10 animals. The colony survived for 6,000 years, but the mammoths suffered from a number of genetic disorders.
Oliver Ryder, director of conservation genetics at the San Diego Zoo Wildlife Alliance, said the study contained important lessons for trying to save species from current extinction. He shows that inbreeding could cause long-term damage.
“The gigantic study allows us to examine that process over thousands of years,” said Dr. Ryder, who was not involved in the new study. “We don’t have data like that for the species we’re trying to save now.”
Dr. Dalén and his colleagues examined the genomes of 14 mammoths that lived on Wrangel Island from 9,210 years ago to 4,333 years ago. The researchers compared the DNA of the Wrangel Island mammoths with seven genomes of mammoths that lived on the Siberian continent until 12,158 years ago.
The genome of any animal contains an enormous amount of information about the population to which it belonged. In large populations there is a lot of genetic diversity. As a result, an animal will inherit different versions of many of its genes from its parents. In a small population, animals 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 on the Siberian continent. Few mammoths spent time there, preferring the lower regions where more abundant plants grew.
But at the end of the ice age, melting glaciers submerged the northern margin of Siberia. “There was a small herd of mammoths that was on Wrangel Island when it became cut off from the mainland,” Dr. Dalén said.
The continent’s mammoths faced significant challenges to their survival. Humans hunted them, while the changing climate wiped out much of their grassland habitat, turning it into tundra.
But the few mammoths stranded on Wrangel Island enjoyed a tremendous stroke of good luck. 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 wonderful place to live,” Dr. Dalén said.
He and his colleagues found that the Wrangel Island population expanded from fewer than 10 mammoths to about 200. That was probably the maximum number of mammoths the island’s plant life could support.
But life was far from perfect for Wrangel’s mammoths. The few animals that founded the island had very little genetic diversity, and Dr. Dalén and his colleagues found that the level remained low for the next 6,000 years.
“They carried with them the inbreeding that they acquired in the early days,” he said.
As a result, mammoths likely suffered from a high level of hereditary diseases. Dr. Dalén suspects that these sick mammoths managed to survive for hundreds of generations because they had no predators or competitors. The Wrangel Island herd would probably have quickly disappeared on the mainland.
The new study does not reveal how exactly Wrangel’s mammoths met their end. There is no evidence that humans are to blame; The first known visitors to Wrangel Island appear to have established a summer hunting camp 400 years after mammoths became extinct.
For now, Dr. Dalén can only speculate about the true cause of the mammoth’s extinction. The war in Ukraine has made it impossible for him and his colleagues to travel to Russia to conduct further research.
It is possible that a fire in the tundra wiped out the Wrangel mammoths, or that an Arctic volcano erupted. Dr. Dalén can even imagine that a migratory bird brought a flu virus to Wrangel Island, which then jumped to the mammoths and wiped them out.
“We still have several possible explanations left and we haven’t been able to narrow them down yet,” he said.
Dr. Dalén believes the new study bodes poorly for conservation biologists trying to rescue species from the brink of extinction. Even if they restore a species to a larger population, it may still be saddled with a low level of genetic diversity.
Dr Dalén said it may be essential to boost the genetic diversity of recovering populations. Conservation biologists have been investigating how to do this – by moving individual animals between populations so they can interbreed, for example.
Cloning could provide another way to help species recover. Dr. Ryder and his colleagues have been freezing cells from endangered animals to preserve some of their genetic diversity. In 2021, researchers managed to produce a clone of a black-footed ferret from a population that had gone extinct in the 1980s.
Without these interventions, an endangered species may have difficulty escaping a legacy of inbreeding, even after hundreds of generations. “You may still have these time bombs in your genome that don’t bode well in the long term,” Dr. Ryder said.