What does it take to survive an ice age? Woolly mammoths are extinct today, but they thrived during the Late Pleistocene era. But what genetic adaptations separate woolly mammoths from their modern-day elephant relatives? To discover this, we analyzed the genomes of 23 woolly mammoths. This included one of the oldest woolly mammoth specimens ever discovered – 700,000 years old! We compared these to the genomes of living Asian and African elephants and looked for unique mutations in woolly mammoth genes. We found that woolly mammoths had changes in genes linked to hair growth and fat storage. These may have helped the woolly mammoth survive in its cold environment. The earliest woolly mammoths already had thick fur coats and large fat deposits. But these and other traits, like small ears, continued to evolve over time.