For millions of years, mammoths lived in Europe, Asia, and North America. Starting about 15,000 years ago, these giant animals began to disappear from their vast range until they survived only on a few islands.
Eventually, mammoths disappeared from these refuges, too, with one exception: Wrangel Island, a landmass the size of Delaware more than 80 miles north of the Siberian coast, where mammoths had survived for thousands of years—they were still alive when the Great Pyramids of Egypt were being built.
When the Wrangel Island mammoth disappeared 4,000 years ago, mammoths became extinct for good.
For two decades, geneticist Lov Dahlen of Stockholm University and his colleagues have been extracting DNA from fossils from Wrangel Island. In recent years, they have assembled the entire mammoth genome. On Thursday, they published a new study release Reconstructing the genetic history of these mysterious animals.
Scientists concluded that the island’s mammoth population was established about 10,000 years ago by a small group of fewer than 10 mammoths. The group survived for 6,000 years, but the mammoths suffered from a variety of genetic diseases.
Oliver Ryder, director of conservation genetics at the San Diego Zoo-Wildlife Alliance, said the study offers important lessons for today’s attempts to save species from extinction. It shows how inbreeding can cause long-term harm.
“This huge study allows us to look at this process over thousands of years,” said Dr. Ryder, who was not involved in the new research. “We don’t have data like this for the species we’re trying to save now.”
Dr. Dahlen and his colleagues studied 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 12,158 years ago.
The genome of any animal contains a wealth of information about the population it belongs to. In large populations, genetic diversity is high. Therefore, animals inherit many different versions of genes from their parents. In small populations, animals breed closely and inherit many identical copies of genes.
The oldest Wrangel Island fossils contained identical versions of many genes. Dr. Dellen and his colleagues concluded that the island was founded by a tiny population of mammoths.
About 10,000 years ago, Wrangel Island was a mountainous region of mainland Siberia where few mammoths lived, preferring lower-lying, more plant-rich areas.
But at the end of the Ice Age, melting glaciers flooded the northern edge of Siberia. “When Wrangel Island was cut off from the mainland, there was a small population of mammoths that happened to be there,” Dr. Dahlen said.
Mammoths on the continent faced enormous challenges to survive. Humans hunted them, and climate change destroyed much of their grassland habitat, turning it into tundra.
But the few mammoths stranded on Wrangel Island were lucky. There were no humans or other predators on the island, and they did not have to face competition from other herbivorous mammals. What’s more, the climate on Wrangel Island made it an ecological time capsule, where mammoths could still enjoy a variety of plants from the Ice Age.
“Wrangel Island is a prime place to live,” Dr. Darren said.
He and his colleagues found that the mammoth population on Wrangel Island grew from fewer than 10 to about 200. That was probably the maximum number of mammoths that the island’s vegetation could have supported.
But life was far from perfect for the Wrangel mammoth. The few animals that founded the island had very low genetic diversity, and Dr. Dahlen and his colleagues found that genetic diversity remained low for the next 6,000 years.
“They inherited early inbreeding,” he said.
Therefore, the mammoths may have suffered from a high rate of genetic diseases. Dr. Dahlen suspects that these diseased mammoths survived for hundreds of generations because they had no natural enemies or competitors. The mammoth herd on Wrangel Island may soon disappear on the mainland.
The new study does not reveal what caused the extinction of the Wrangel Island mammoths. There is no evidence that humans were to blame; the first known humans to visit Wrangel Island appear to have established summer hunting camps 400 years after the mammoths went extinct.
For now, Dr. Darren can only speculate on the real cause of the mammoth’s extinction. The war in Ukraine has prevented him and his colleagues from traveling to Russia to conduct further research.
It’s possible that tundra fires killed the Wrangel mammoths, or that an Arctic volcanic eruption led to their extinction. Dr. Dahlen could even imagine that a migrating bird brought the flu virus to Wrangel Island, which then passed to the mammoths, causing their extinction.
“We still have many possible explanations, but we still can’t narrow it down,” he said.
Dr. Darren believes the new research bodes badly for conservation biologists trying to save species from extinction. Even if they can restore a species to a larger population, it may still be burdened with low levels of genetic diversity.
Dr Darren said boosting genetic diversity in recovering populations could be crucial. Conservation biologists have been investigating how to do this – for example, by moving individual animals between populations so they can interbreed.
Cloning may offer another way to restore species. Dr. Ryder and his colleagues have been freezing cells from endangered animals to preserve some of their genetic diversity. In 2021, researchers successfully bred clone This is a species of black-footed ferret, which became extinct in the 1980s.
Without these interventions, it may be difficult for an endangered species to shake off the legacy of inbreeding, even after hundreds of generations. “It may still have these time bombs in its genome, which doesn’t bode well for the long term,” Dr. Ryder said.
