A couple million years ago, mammoths migrated north from Africa to colonize Eurasia. Sometime around then a massive ice age kicked in—and it was stay warm or die. So their tails and heat-shedding ears shrunk, and they grew thick coats of oily fur. 

But if you're out in the cold all day you also need some biochemical adjustments. Hemoglobin is the protein in red blood cells that delivers oxygen to your tissues. And it doesn't off-load oxygen well at low temperatures; it just clings to it more tightly. So mammoths solved that problem by evolving hemoglobin that releases oxygen more easily in the cold. That’s according to a study published in the journal Nature Genetics. 

Researchers got the DNA that codes for hemoglobin from a 43,000-year-old mammoth specimen. They then used E. coli bacteria to produce actual mammoth hemoglobin. Then they compared mammoth hemoglobin to that of their living cousins, Asian elephants, at 37, 25 and 10 degrees Celsius. Due to just a few key structural changes, mammoth hemoglobin can release oxygen more readily at cold temperatures. Which was just the thing to help mammoths keep their cool.

—Christopher Intagliata