I remember that quite a long time ago a bit of crackpot academic of some sort made a study into this. His theory was that all animals have a finite amount of heartbeats and when they run out you will die. He came to this conclusion after looking at animal size, animal heart rate and animal life expectancy, ie, the smaller the animal, the faster it's heart beats and the shorter it's life expectancy.
He laid out all of the figures starting with mice, then rats, then domestic cats and on and on right up to gorilla's and elephants and his argument based on his figures appeared to be quite rational. After reading his research papers another academic jokingly said what he appears to be saying is with regard to a finite quantity of heartbeats theory is, don't run when you can walk, don't stand when you can sit and don't sit when you can lie down.
Who knows, maybe he had a point.
Iain.