10,000 years ago, when sea levels rose and Wrangel Island off the coast of Siberia became separated from the mainland, the last population of woolly mammoths, numbering no more than eight individuals, became completely isolated.
That group, which grew to 200 or 300 individuals in 20 generations, survived on the island for another 6,000 years despite its inbreeding and low genetic diversity, so this would not be the reason for its extinction, according to a study published this Thursday (06/27/2024) by the journal Cell.
With the end of the Ice Age, the dry steppe tundra in which mammoths had thrived gradually transformed, from south to north, into wetter temperate forests amid rising global temperatures, confining these animals to the northernmost reaches of Eurasia.
Its extinction remains a mystery.
“What happened in the end remains a mystery: we don’t know why they became extinct after having been more or less fine for 6,000 years, but we think it was sudden,” says one of the study’s lead authors, Love Dalén, an evolutionary geneticist at the Centre for Palaeogenetics in Stockholm, Sweden.
However, thanks to the results of this study, “we can confidently reject the idea that the population was simply too small and that they were doomed to extinction for genetic reasons,” he emphasizes.
They suffered mutations, but these disappeared
According to the researchers, mammoths slowly accumulated moderately harmful mutations. But the most harmful defects disappeared from the population, apparently because individuals carrying these mutations were less likely to survive and reproduce.
“This suggests that something else, and very sudden, caused the population collapse,” says evolutionary geneticist and co-author Marianne Dehasque of Uppsala University in Sweden.
Human participation?
The authors of the research also ruled out that the complete disappearance of the woolly mammoth was due to human hunting: “From archaeological evidence, we know that humans did not arrive until 400 years after the mammoths became extinct,” adds Dehasque.
Dalén, for his part, believes that if this had happened, “it would be easy to find homes and habitation structures, as well as fragments of flint, reworked bones and tusks, etc. But at Wrangel there is no trace of human interaction with mammoths.”
The mammoths “were unlucky”
Other possible causes of extinction that are raised are an infectious disease, possibly brought to the island by birds, or that they have not had more plants to eat.
“Perhaps mammoths would have been vulnerable to it, given the reduced diversity we identified in the immune system genes,” Dalén says. But also, a “really bad” weather season would have caused “a really bad year of growth for the Wrangel plants. Given how small the population was, it would have been vulnerable to such random events.”
“In other words, it seems to me that perhaps the mammoths simply had bad luck. If it had not been for that bad luck, perhaps we would still have mammoths today,” Dalén concludes.
JU (efe, rtre)
