Why does an elephant live twenty times longer than a mouse? Partly just because it's bigger, but even after correcting for body mass, mammals with fast metabolic rates (high oxygen consumption), such as mice, age and die swiftly, whereas animals with slow metabolic rates, such as elephants, live longer and age more slowly.
While an inverse correlation between resting metabolic rate and longevity in animals generally holds true, there are some exceptions to the rule. Birds, bats, and humans live several times longer than their metabolic rates would suggest. The reason lies in the rate at which reactive oxygen species (ROS) leak out of the mitochondrial respiratory chain, the succession of membrane-bound proteins that passes electrons from NADH to oxygen. According to Gustavo Barja at the Complutense University in Madrid, pigeons leak barely a tenth the ROS of rats, and live nearly ten times longer, yet their resting metabolic rates ...
