An island refuge at the end of an age
After the last Ice Age, as glaciers retreated and sea levels rose, most of the world's woolly mammoths (Mammuthus primigenius) vanished. By about 10,000 years ago, they were gone from the mainlands of Siberia and North America. But one population held on. On Wrangel Island, a remote piece of land in the Arctic Ocean, a small group of mammoths was cut off from the mainland by the rising waters. This isolation created a unique environment, allowing the species to survive for another 6,000 years.
Radiocarbon dating of remains found on the island shows that these mammoths persisted until about 4,000 years ago, or 2000 BCE. This means they were still alive during the construction of the Great Pyramids of Giza in Egypt and the flourishing of Bronze Age civilizations in Mesopotamia. The population on the island was small, likely numbering only a few hundred individuals at any given time. This small population size, combined with thousands of years of isolation, had severe genetic consequences.
The genomics of extinction
The DNA extracted from the bones and teeth of the Wrangel Island mammoths shows a "genomic meltdown." Scientists compared the genome of a 4,300-year-old Wrangel Island mammoth with that of a 45,000-year-old Siberian mammoth. The results revealed that the island mammoth had many harmful genetic mutations.
Due to intense inbreeding, deleterious genes that would normally be weeded out in a larger population became common. These mutations affected basic biological functions. For example, the mammoths had mutations that caused a loss of olfactory receptors, impairing their sense of smell. This would have made it harder to find food and mates. Other mutations were linked to reduced male fertility, neurological defects, and even changes to their hair, giving them a satiny, less-insulating coat. While these genetic defects were not the single cause of their final extinction—a sudden event like a harsh winter or disease is also possible—they left the population vulnerable.