The final refuge
Wrangel Island, a remote outpost in the Arctic Ocean, holds the distinction of being the last place on Earth where woolly mammoths survived. While mainland populations of Mammuthus primigenius vanished around 10,000 years ago, a small group found a temporary sanctuary here. Rising sea levels following the last ice age isolated the island from Siberia, trapping a few hundred mammoths. They continued to live on this Arctic refuge for another 6,000 years, finally disappearing around 4,000 years ago, contemporaneous with the construction of the Great Pyramid of Giza.
The Wrangel Island mammoths were smaller than their mainland ancestors, with shoulder heights ranging from 180 to 230 cm, but they are not considered true dwarfs. Their remains, scattered across the tundra and in riverbeds, provide a record of the final millennia of a species. The island itself is a Pleistocene-era ecosystem, having escaped glaciation during the last Ice Age, which preserved its ancient tundra landscape and a high diversity of plant species.
A genomic death spiral
The isolation that kept the mammoths from mainland threats eventually led to their extinction. With a population estimated at only a few hundred individuals, the animals entered a state of "genomic meltdown." Analysis of a 4,300-year-old Wrangel mammoth genome revealed an accumulation of harmful mutations compared to a 45,000-year-old Siberian specimen.
This genetic decay manifested in several ways. Scientists identified mutations that likely resulted in a satiny and translucent fur coat with less effective insulation. Other genetic defects suggest a reduced sense of smell due to a loss of olfactory receptors and altered urinary proteins, which could have disrupted social structures and mate selection, as these are important for communication in modern elephants. This collection of detrimental genetic changes, caused by severe inbreeding in a tiny population, shows a nearly-neutral model of evolution, where negative mutations can accumulate rapidly when population sizes are small. While some recent studies suggest the population was stable until a sudden event, the evidence of genetic decay is clear in the mammoth remains. The first evidence of humans on the island dates to centuries after the mammoths had already disappeared.