[hnu234]

> Eating more and exercising more (and the energy required to keep your core temperature up) might kill you faster, maybe through free radical production from metabolism.

There's a theory that it's actually heartbeats. Most animals have about 1.5 billion heartbeats.

"The reason an elephant lives longer than a shrew is not because its heart beats longer. It's because its heart beats slower. So it takes a few more years for the elephant to complete his or her up to one and a half billion beats."

https://www.npr.org/2007/08/18/12877984/size-matters-the-hid...