About 4,000 years ago, the last of Earth’s woolly mammoths died out on a lonely Arctic Ocean island off the coast of Siberia, a melancholy end to one of the world’s charismatic Ice Age animals. But what doomed this last mammoth population on Wrangel Island? A new genomic analysis deepens the mystery.
The study offers the fullest account to date of the inbreeding, deleterious mutations and low genetic diversity experienced by this population during 6,000 years of isolation on the island but concluded that, despite previous suggestions, these factors are unlikely to have doomed the Wrangel mammoths.
“This suggests that something else, and very sudden, caused the population to collapse,” said evolutionary geneticist Marianne Dehasque of Uppsala University in Sweden, lead author of the study published on Thursday in the journal Cell, opens new tab.
The researchers examined genome data obtained from the remains of 14 Wrangel mammoths and seven mammoths from a Siberian mainland population ancestral to the island dwellers, dating to up to 50,000 years ago.
As the Ice Age eased, the dry steppe tundra where mammoths long had thrived transformed, gradually from south to north, into wetter temperate forests amid rising global temperatures, confining these animals to Eurasia’s northernmost reaches.
“This is probably also how mammoths eventually ended up and became isolated on Wrangel Island, which lost its connection to the mainland around 10,000 years ago due to rising sea levels. It may have even been a single herd that populated the island,” Dehasque said.
The genome data indicated that the population isolated on mountainous Wrangel originated with at most eight individuals, then grew to 200 to 300 mammoths within about 20 generations – around 600 years – and remained stable.
The study detected reduced diversity in a group of genes crucial to the immune system. But while the mammoths slowly accumulated moderately harmful mutations, the most deleterious defects were disappearing from the population, apparently because individuals carrying these were less likely to survive and reproduce.