A 6,000-year epilogue
While most woolly mammoths (Mammuthus primigenius) vanished around 10,000 years ago, one isolated group found a final refuge. Rising sea levels after the last Ice Age stranded a small herd on what is now Wrangel Island, a remote outpost in the Arctic Ocean. This population survived for another 6,000 years, finally disappearing around 4,000 years ago. Their existence means these mammoths were contemporaries of ancient civilizations; the Great Pyramid of Giza was already complete when the last mammoth died.
The island became a genetic prison. The population, which stabilized at around 200 to 300 individuals, suffered from extremely low genetic diversity. Scientists compared the genome of a 4,300-year-old Wrangel Island mammoth with that of a 45,000-year-old mainland specimen. The results showed a "genomic meltdown" in the island population. The small gene pool led to severe inbreeding, allowing a host of harmful mutations to accumulate that would normally be eliminated by natural selection in a larger population.
The genetics of extinction
The catalog of genetic defects found in the Wrangel Island mammoths reveals a population in crisis. They had numerous deletions in their genetic code and an excess of premature stop codons, effectively breaking certain genes. Specific mutations were identified that had deep consequences. For instance, multiple mutations affected their sense of smell; one gene, OR5A1, helps with detecting the floral scents of roses and violets. This sensory impairment would have made it harder to find food and mates.
Mutations also affected male fertility and development. One of the most striking findings relates to two independent mutations in a gene called FOXQ1. In mice, these mutations are known to cause a glossy, satin coat that is structurally weaker and offers poorer insulation—a serious defect in an Arctic climate. These "satin mutants" in other species are also known to suffer from digestive problems, suggesting the mammoths may have had constant gastric trouble. This cascade of accumulating deleterious genes is an "extinction vortex," where a shrinking population's declining genetic health accelerates its own demise.