One Billion Heartbeats (opens in new tab)

I consider this to be an instance of the old adage (Mar's law) that "everything is linear if plotted log-log with a fat marker".

Edit: fixed a typo.

On the first chart, we see that humans are definitely an outlier. Slide us back to the left and see where we would "naturally" be without modern medicine and we should live around 35 years. This lines up nicely with historical data[1].

[1] http://en.wikipedia.org/wiki/Life_expectancy#Life_expectancy...

So that suggests I should work out at little as possible so my 1 billion heartbeats last 200 years instead of 75?

It took about 10 seconds for me to stop searching for the X button to close the popup and realize this is how the site is laid out.

In July 1969, just before the first manned lunar landing, Life magazine had a special issue about the astronauts. Many of the astronauts were profiled. All of them did some sort of athletics --- running, racketball, etc. --- except for Neil Armstrong, who was quoted as saying (paraphrasing from memory): I believe every man comes into this world with a finite number of heartbeats allocated to him, and I'm damned if I'm going to waste any of mine running around doing exercises.

I thought that it's a pretty well known fact that small dogs live longer. Can't find a really good link, but this one is OK: http://pets.webmd.com/dogs/features/dogs-and-life-span-which...

Some notes: Birds follow a slightly different power law and consequently live much longer. However, they do still follow a similar relationship.

Interesting exceptions in mammals are humans and (surprisingly) bats, both of which beat the curve pretty dramatically. Several mechanisms have been proposed for this exception including brain size and several specific proteins.

If anyone is interested in some more mechanistic or literature driven explanations, here is a good starting point http://www.ncbi.nlm.nih.gov/pmc/articles/PMC128563/

This was a 'fun fact' I was told at a young age. I'm not ashamed to admit that I took it literally and spent a few months of my childhood fearing anything that made my heart race.

Actually, there is a physical mechanism in cellular life that sets a lifespan limit, by roughly constraining the number of replications most differentiated cell lines in a body can support. Thus the correlation between slower metabolism and longer lifespan. The 'number of heartbeats' observation is a consequence of that correlation.

The mechanism is a little too complicated to describe accurately here. You can find a great deal on it with google search terms "telomere fraying" or "telomere fuse".

Very roughly, every chromosome has a 'telomere' structure at each end that acts to prevent the DNA double helix strands from 'fraying'. In the single cell embryo these structures are several thousand bases long. In every cell division after that, some random number of the telomere bases fail to be replicated. So the telomeres get shorter and shorter with each replication. In a cell where the telomere is all gone on a chromosome, genes at the end of that chromosome get progressively destroyed - thus (depending whether it's an active gene) wrecking some aspect of the cell's metabolism. With many different chromosomes (eg 26 in humans), 2 ends per chromosome, shifting gene arrangements, huge statistical populations of cells with individual telomere failures, and multiple lines of differentiated cells all replicating at differing rates, it's no wonder 'aging' shows such complex and variable symptoms.

I suspect if someone did a study of multiple species examining embryonic telomere lengths, average telomere loss per cell replication, replication (metabolic) rate, and average lifespan, there'd be a function of those factors giving a much more precise connection than 'number of heartbeats'.

There is a great paper written by Geoffrey West called "Life's Universal Scaling Laws" http://biology.unm.edu/jhbrown/Documents/Publications/West&#...

I was under the impression he was one of the first to touch on this topic, so I find it weird he wasn't listed.

He also applied this to city growth. Which is much more interesting, considering cities aren't biological, strictly speaking.

http://www.nytimes.com/2010/12/19/magazine/19Urban_West-t.ht...

I feel for the hamsters. I'd have a 400+ bpm too if I knew I'd only live for 3 years.

But being serious, I'd like to see the the variance on those numbers. Bpm's of ~60 are normal for some, while others hover around ~90+. So within the range of what's considered a normal heartrate (60 - 100), numbers can vary by as much as 66%.

On a pet peeve tangent... I dislike the "Six Sigma" meme because, having a semimechanical heart, one-in-a-million failures would mean I'd be dead by now. I need one-in-a-billion reliability at minimum.