Mammoths had more than woolly coats to protect them from the frigid conditions of their sub-zero stomping grounds, scientists have discovered.
The extinct beasts had a form of antifreeze blood that kept their bodies supplied with oxygen in the sub-zero temperatures, according to a study of DNA extracted from 43,000-year-old mammoth remains.
A genetic adaptation in the woolly mammoths' haemoglobin - the molecular cage that carries oxygen in the blood - allowed them to thrive at high latitudes without losing much heat.
Ancestors of the woolly mammoth originated in equatorial Africa about seven million years ago, but populations migrated north more than one million years ago, in a period of Earth's history when climate change caused temperatures to plummet.
Unlike modern elephants, which have evolved large ears and other characteristics to keep cool in excessive heat, ancestral mammoths survived by evolving ways of saving heat, such as small ears and tails.
In the latest study, a team led by Kevin Campbell at the University of Manitoba in Canada found another physiological trick that mammoths used to endure the ice age. Campbell's team isolated haemoglobin DNA from a woolly mammoth recovered from the Siberian permafrost and compared it with genetic code extracted from modern African and Asian elephants.
The mammoth's DNA differed in a small but significant way. Changes in one percent of the proteins studied showed that it took less energy for mammoth haemoglobin to release its oxygen into the body as it coursed through the blood vessels. “It literally allows their blood to run cold,” Mr. Campbell said.
“Without this genetic adaptation, woolly mammoths would lose more heat in winter, and they would have to replace that energy by eating more. In winter, there is less food around, so it was clearly a benefit to have this.” The research is reported in the journal Nature Genetics.
Current Arctic species, such as musk ox and reindeer, have evolved a similar antifreeze system independently.
Mr. Campbell said the work shows how paleobiology - broadly the study of ancient, extinct life - has come of age. “We resurrected mammoth haemoglobin. It's no different from going back 40,000 years in a time machine and taking a blood sample from the animal.”
Michi Hofreiter, a co-author of the study at the University of York, said: “Our study is the first one to reconstruct an evolutionary important, adaptive trait from an extinct species using ancient DNA. It therefore opens up the possibility to build up a much more complete picture of morphology, physiology and evolutionary adaptations than would be possible using non-molecular study of fossil bones.”