The planet’s last surviving mammoth population was killed by a mysterious, random and unexpected event, a new study has found.
The population, isolated from the rest of the world for 6,000 years on Wrangel Island in what is now Russia’s extreme north, was previously believed to be slowly disappearing from genetic inbreeding.
But a new study has revealed that the population – which grew from a maximum of eight individuals to 300 before its demise 4,000 years ago – did not disappear for genetic reasons. This leaves an even bigger mystery as to what actually happened. The researchers published their findings June 27 in the journal Cell.
“We can now confidently reject the idea that the population was simply too small and that they were doomed to extinction for genetic reasons,” senior study author Love Dalén, an evolutionary geneticist at the Center for Paleogenetics in Stockholm, said in a statement. . “That means it was probably just a random event that killed them off, and if that random event hadn’t happened, then we’d still have mammoths today.”
From about 300,000 to 10,000 years ago, woolly mammoths roamed the cold plains of Europe, Asia, and North America. As the ice in these northern regions melted, the Arctic tundra on which the giant pachyderms relied for food disappeared. This caused the mammoths’ range to shrink until they eventually became extinct.
But sometime during this time period, a small group of mammoths crossed the ice on the northwest coast of Siberia and began to inhabit Wrangel Island, becoming cut off from the population on the mainland after the ice bridge disappeared about 10,000 years ago. Isolated on the frozen island, the mammoths there survived for another 6,000 years.
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Because the Wrangel Island mammoths originated from at most eight individuals, scientists previously believed that deleterious mutations due to inbreeding could have caused the animals’ deaths.
To examine the consequences of the Wrangel Island strait, researchers in the new study used DNA extracted from bones and tusks to analyze the genomes of 21 mammoths — 14 from the island and seven from the mainland population before the impasse occurred.
They found that the island’s woolly mammoths did show signs of inbreeding and low genetic diversity, but their mutations were only moderately harmful and the most dangerous were slowly being purged from their genomes.
“If an individual has an extremely deleterious mutation, it’s basically not viable, so those mutations gradually disappeared from the population over time,” study first author Marianne Dehasque, an evolutionary geneticist at the Center for Paleogenetics. “But on the other hand, we see that mammoths were accumulating mild deleterious mutations almost until they went extinct.”
With the exception of inbreeding, the true cause of death of these woolly mammoths is still unknown, the researchers said.
“What happened at the end is still a mystery – we don’t know why they disappeared after being more or less fine for 6,000 years, but we think it was something unexpected,” Dalén said. “I would say there is still hope of understanding why they disappeared, but no promises.”
To investigate further, the researchers will look for clues in unearthed mammoth fossils from the last 300 years of population on the island. Meanwhile, scientists say their findings are useful for understanding the ongoing diversity crisis, as the mammoth’s grim fate is mirrored by many populations today.
“It’s important that today’s conservation programs keep in mind that it’s not enough to grow the population back to a decent size,” Dehasque said. “You also have to monitor it actively and genetically because these genomic effects can last for more than 6,000 years.”