
One Billion Heartbeats - jchavannes
http://skeptics.stackexchange.com/questions/5701/does-every-species-get-around-a-billion-heartbeats-on-average
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InclinedPlane
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.

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webmasterm
Took me a second to understand that you meant "marker" not "market".

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InclinedPlane
Damnit, fixed.

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TerraHertz
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'.

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juan_juarez
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...](http://en.wikipedia.org/wiki/Life_expectancy#Life_expectancy_variation_over_time)

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TeMPOraL
Except "historical data" is not what where we would "naturally" be, since life
expectancy is dragged down by high child mortality rate.

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balsam
Not to be snarky, but what are the child mortality rates for a monkey or a
hamster?

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bgilroy26
This doesn't answer your question, but when we evolved to walk upright a
significant level of risk was added to childbirth.

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tolos
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.

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khet
That was torture. I wish I was kidding.

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dctoedt
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._

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landhar
Apparently, according to wikiquote it's misattributed to him:

<http://en.wikiquote.org/wiki/Neil_Armstrong#Misattributed>

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dctoedt
Then _Life_ magazine was among the misattributors; I read the quote when it
was published (and was delighted, because it matched my own attitude about
athletics).

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landhar
I am as disappointed as you are. I found this note on wikiquote as I was
looking for the original reference.

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isalmon
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...](http://pets.webmd.com/dogs/features/dogs-and-life-span-which-breeds-
live-longest)

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jtheory
That "stat" surprised me as well -- small dogs @ 10 years and large ones at
17? Uh, no.

Great danes and Irish wolfhounds (and other big breeds as well, AFAIK) only
average something sad like 7 years, whereas those little yappy toy poodles
average twice that.

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philsalesses
There is a great paper written by Geoffrey West called "Life's Universal
Scaling Laws"
[http://biology.unm.edu/jhbrown/Documents/Publications/West&#...](http://biology.unm.edu/jhbrown/Documents/Publications/West&Brown2004PT.pdf)

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...](http://www.nytimes.com/2010/12/19/magazine/19Urban_West-t.html?pagewanted=all&_r=0)

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kyro
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%.

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cdcox
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/>

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jaggederest
Yes I was shocked to find out that parrots run an average heartrate of 350 bpm
or so, for 40 years. 7 billion heartbeats.

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ctdonath
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.

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ortusdux
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.

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huggah
Considering that fear does just that, this seems like a miserable existence.

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

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cfj
But working out lowers your resting heart rate. So you should work out as much
as you can!

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jspaur
This would be a fun one to work through. If 100 hours of working out reduced
your heart rate by 1bpm (I have no idea if this is true, just sounds
plausible), but during workouts you increased your BPM by 20%, where is the
equilibrium?

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Someone
I think you will need to refine your model. At the least, you will have to
have some way to limit resting heart rate to be > 0\. Alternatively, your
model suggests that person will die from 6000 hours of practice, as it would
bring his resting heart rate down to zero. If you don't, your optimization run
would say something like "work out for 1,000,000 hours at a cost of
100,000,000 heart beats or so. Then, enjoy an infinite life with negative
resting heart rate and even lower heart rate during exercise."

You also will want to model the fact that your resting heart rate does not
stay at a lower level forever after exercise.

Finally, but that's peanuts compared to the other problems: let's start with a
starting rest rate of 60 BPM. Exercise for 1000 hours to bring it back to 50
BPM, and your heart rate during workouts becomes 1.2 x 50 BPM = 60 BPM?
Unlikely.

