The planet’s last surviving mammoth population was killed by a random and sudden mysterious event, a new study has revealed.
A population isolated from the rest of the world for 6,000 years on Wrangel Island in present-day extreme northern Russia was previously believed to slowly exterminated by genetic inbreeding.
But the new study found that the population – which grew from a peak of eight individuals to 300 before its extinction 4,000 years ago – did not go extinct for genetic reasons. This leaves even more of a 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 it was doomed to extinction for genetic reasons,” lead study author Love Dalén, an evolutionary geneticist at the Center for Paleogenetics in Stockholm, said in a statement. “That means it was probably just some random event that killed them, and if that random event hadn’t happened, then we’d still have mammoths today.”
About 300,000 to 10,000 years ago, woolly mammoths roamed the frigid plains of Europe, Asia, and North America. As the ice in these northern regions melted, the arctic tundra that the giant pachyderms relied on for food disappeared. This caused the mammoths to shrink in range until they eventually disappeared.
However, sometime during this time period, a small group of mammoths crossed the ice on the northwestern coast of Siberia and began to inhabit Wrangel Island, becoming cut off from the mainland population once the ice bridge disappeared 10,000 years ago. Alone on a frozen island, the mammoths survived there for another 6,000 years.
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Because the mammoths on Wrangel Island came from no more than eight individuals, scientists previously thought that deleterious mutations caused by inbreeding may have caused the animals’ demise.
To gain insight into the consequences of the Wrangel Island bottleneck in the new study, researchers 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 bottleneck occurred.
They found that the island mammoths did show signs of inbreeding and low genetic diversity, but their mutations were only moderately harmful, and the most dangerous ones were slowly removed 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, said in a statement. “But on the other hand, we see that mammoths accumulated mildly deleterious mutations almost to the point of extinction.”
Barring inbreeding, the actual cause of death for these mammoths is still unknown, the researchers said.
“What happened at the end is still a bit of a mystery – we don’t know why they went extinct after being more or less fine for 6,000 years, but we think it was something sudden,” Dalén said. “I’d say there’s still hope to find out why they went extinct, but no promises.”
For further investigation, the researchers will look for clues in the discovered mammoth fossils from the last 300 years of population on the island. Meanwhile, the researchers say their findings are useful for understanding the ongoing diversity crisis, as the mammoth’s grim fate mirrors that of many contemporary populations.
“For current conservation programs, it’s important to remember that it’s not enough to get the population back to a decent size,” Dehasque said. “You also have to monitor it actively and genetically, because these genomic effects can last over 6,000 years.”