Its in their blood..

Here's a really cool science story, researchers working at the University of Manitoba have recreated woolly mammoth blood from DNA extracted from frozen specimens. DNA was first converted to RNA and then replicated in bacteria cells, the protein haemoglobin was then extracted and compared with the same protein in modern elephants. Interestingly and perhaps not surprisingly that haemoglobin was found to have improved efficacy at low temperatures, obviously this would have been a huge selection advantage for a species that lived in cold environments like mammoths.

Its a sobering thought that here we have a species that was widespread and well adapted for life in it's icy habitats and yet it still went extinct, as is evident from this example, the only reliable constant in life is change.