The last woolly mammoths were impressively inbred—but that’s not what killed them

Despite multiple attempts to resurrect woolly mammoths, the ancient animal species currently remains very much extinct. Their last known population—a group isolated by rising sea levels on Wrangel Island off the Siberian coast—managed to survive 6,000 years before finally disappearing roughly 10,000 years ago. But unlike the dinosaurs, what specifically caused the Wrangel mammoths to ultimately die out still remains a mystery. Thanks to new analysis of 21 separate mammoth genomes, however, at least one theory is likely debunked for good: low genetic diversity.

According to a study published on June 27 in Cell, Swedish Museum of Natural History and Stockholm University researchers collaborating at the Centre for Palaeogenetics can now conclude the woolly mammoth was never “doomed to go extinct for genetic reasons.”

“We can now confidently reject the idea that the population was simply too small,” senior author and evolutionary geneticist Love Dalén continued in an accompanying statement. “This means it was probably just some random event that killed them off, and if that random event hadn’t happened, then we would still have mammoths today.”

But that didn’t mean the last mammoths weren’t impressively inbred by the time of their demise. To reach their conclusion, the team assessed genomic samples from 14 Wrangel mammoths next to another 7 collected from mainland mammoths that predate the island’s isolation. The 21 individuals roughly spanned the species’ final 50,000 years of existence, offering valuable insights into their last generational shifts before extinction.

After reviewing the collected data, Dalén and collaborators determined that Wrangel’s population initially started with at most 8 mammoths, yet managed to grow to somewhere between 200-300 animals within 20 generations despite clear signs of inbreeding and low genetic diversity. The team also discovered a reduced diversity in what’s known as the major histocompatibility complex, a genetic set crucial in vertebrate immune responses. But despite this, population size appears to have remained largely stable until the mammoth’s final days—an indication that the many harmful mutations resulting from inbreeding were weeded out over the generations.

“If an individual has an extremely harmful mutation, it’s basically not viable, so those mutations gradually disappeared from the population over time,” Marianne Dehasque, the paper’s first author and a researcher at the Centre for Palaeogenetics said in a statement. “[B]ut on the other hand, we see that the mammoths were accumulating mildly harmful mutations almost up until they went extinct.”

Apart from crossing off at least one extinction theory from the list, researchers say mammoth genetic analysis could prove useful in conservation efforts for today’s endangered species.

“Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens from a genetic point of view when a species goes through a population bottleneck because they mirror the fate of a lot of present-day populations,” Dehasque continued.

Going forward, the team intends to examine genomic samples from some of the very last woolly mammoths to ever walk the Earth, down to within the last 300 years of their existence. Further information could finally close the case on what doomed mammoths—but Dalén cautions that experts may never land on a definitive answer. Although the team thinks it was “something sudden,” he adds that “what happened at the end is a bit of a mystery still.”

“I would say there is still hope to figure out why they went extinct, but no promises,” Dalén said.