I ran across this one last week on a Discover Magazine science blog: Ten Things Everyone Should Know About Time.
There were a number of physics type entries, but it was the last one that intrigued me:
10. A lifespan is a billion heartbeats. Complex organisms die. Sad though it is in individual cases, it's a necessary part of the bigger picture; life pushes out the old to make way for the new. Remarkably, there exist simple scaling laws relating animal metabolism to body mass. Larger animals live longer; but they also metabolize slower, as manifested in slower heart rates. These effects cancel out, so that animals from shrews to blue whales have lifespans with just about equal number of heartbeats - about one and a half billion, if you simply must be precise. In that very real sense, all animal species experience "the same amount of time." At least, until we master #9 and become immortal.
I must quibble a bit about the blog post, however. The author, Sean, states that a "A lifespan is a billion heartbeats" in the header for his para 10, then in the body he says "...about one and a half billion, if you simply must be precise." Also, if you Google "heartbeats in lifetime" you'll see a bunch of results that, without clicking thru, would seem to be mutually exclusive.
That's quite a difference, and I can't speak to the math, and it kinda sounds too much like pop science. That said, let's suspend our disbelief and go with the bigger picture here. Namely, that the notion of an allotted number of heart beats, while not new, does sound rather intriguing.
See, we endurance athletes bank our heartbeats. Sure, when we do some heart-pounding, leg-quivering ascent and our heartbeats soar to 200 or whatever your personal max is, it seems that you're squandering those precious beats. Until you consider that your heart rate is only elevated for a few hours for a long run, then it drops back to your fit resting rate of what--40s? 50s?--for the rest of your existence.
That's a good trade off.
What will you do with your billion to 1.5 billion heartbeats? I think I'll go trail running.