
Your body wasn’t built to last: a lesson from human mortality rates - aespinoza
http://gravityandlevity.wordpress.com/2009/07/08/your-body-wasnt-built-to-last-a-lesson-from-human-mortality-rates/
======
reasonattlm
The body can be considered as a system of many redundant components, with
aging as the result of progressive unrepaired damage to those components. This
is a model that works very well. For further reading, you might look at the
application of reliability theory to aging:

[http://www.fightaging.org/archives/2010/05/applying-
reliabil...](http://www.fightaging.org/archives/2010/05/applying-reliability-
theory-to-aging.php)

[http://en.wikipedia.org/wiki/Reliability_theory_of_aging_and...](http://en.wikipedia.org/wiki/Reliability_theory_of_aging_and_longevity)

Once you start to think along the lines of damage and repair, you inevitably
end up in the SENS camp. It's the logical place to be.

[http://www.fightaging.org/archives/2006/11/the-engineers-
vie...](http://www.fightaging.org/archives/2006/11/the-engineers-viewpoint-
treat-change-as-damage.php)

Bodies are complex systems and all complex systems can be prolonged in their
period of prime operation by sufficiently diligent incremental repair.
Developing a toolkit to do that for humans is the point of SENS the research
program, with the point of SENS the advocacy program being to help people
understand that the scientific community well understands in detail what needs
repairing.

For more on the biochemistry of damage-that-causes-aging, explained for
laypeople, you might look here:

<http://www.sens.org/sens-research/research-themes>

~~~
hallman76
We need to "gamify" this research. Farmville carrot-growers could be solving
humanity's greatest problem!

(I'm totally serious)

~~~
possibilistic
I'm a computational biochemistry student, and I don't think this is possible.
We can gamify protein folding because this is a well-understood, well-
characterized problem. What we don't have the slightest clue about is how to
restore original cell state, eg. rid cells of aggregate intracellular waste,
repair non-trivial DNA damage, restore the extracellular metabolome, etc.

I think we should stop funding/granting scholarships to liberal arts majors.
Let them become STEM majors.

~~~
ebiester
There are really intelligent people out there who could never pass a calculus
class, much less thermodynamics. Do you want them in your program taking up
all the time of the teacher, stopping those proficient in math from getting
the education they deserve?

~~~
hessenwolf
No there aren't; that's daft. What are you basing that on?

Sure, it might be less easy for some than others, and less motivating, but if
they can learn A, they can learn B and vice versa.

~~~
ebiester
I'm basing it on both my time as a math tutor for Pima Community College and
on people I have known.

People like my mother who, if she can quantify the data she can effectively do
algebra, but as soon as X and Y appear she shuts down. She cannot make the
jump to the abstract thinking of math, and it curtailed her ability to go back
to college. It didn't help that her math teacher in 9th grade told her that
she would never be good at math, much like many women from poor backgrounds.
(I have no study, only the experience in tutoring on how many women said that
a teacher told them not to bother, and could never make it over that hump.)
Now you say that it's merely psychological for them and that they could. I'm
telling you that for as much work as some of these people I tutored put in,
they had a mental block that they simply could not overcome, fighting their
way to a C in college algebra so they could get to where they're going.

I can give as an example my boyfriend, who can speak and teach two languages
better than most people here can in their native language, and is a promising
Ph.D candidate in his program. He worked for a month straight (with my help)
to raise his GRE math to a minimum score. His limit may be calculus, but
certainly not higher math, and not upper level sciences. Yet I have seen this
man wake up, read, write, sleep, and repeat for weeks straight.

He's a gifted writer and academic, but even if he could muddle through
(say...) managed information systems, he'd never be more than mediocre because
his brain simply does not work that way. (He still asks for help with his
Mac.) Square peg, round hole.

It doesn't benefit those who have a passion for the sciences to put him and
dozens of others in the same class, wearing down the professor because they
struggle to grasp concepts that future scientists understood in fifth grade.

~~~
hessenwolf
1\. I worked for a few years in the remedial math centre for mature students
in my university, and one of my best friends did his doctorate in teaching
mature students mathematics. Based on my experience, had I taken your attitude
then I would have just not shown up for work.

2\. I disagree that it doesn't benefit the stronger students. It was awfully
hard for me to learn to teach mathematics, because I had never really had to
learn it in a step by step way myself. However, when I did learn to teach an
area, my understanding was orders of magnitude higher because I had the
understanding of somebody gifted in the area but the method and the attention
to detail of somebody who has learned it the hard way. If you mix classes with
high and low skilled students, you just have to make sure you rely on the high
skilled students as a teaching resource.

~~~
ebiester
1\. Just because I didn't believe they could do differential equations doesn't
mean that I didn't believe they could learn college-leve. algebra with some
coaching. I had more faith in them than they did of themselves, in many cases.

2\. There have been many studies that have tried what you say. The problem is
that the class must go slower to accommodate the slower students. Engineering
degrees already have so much packed into them that they often can't take
classes of interest -- are we going to make it even longer?

------
panic
You can find the original, less ad-encrusted version of this article at
[http://gravityandlevity.wordpress.com/2009/07/08/your-
body-w...](http://gravityandlevity.wordpress.com/2009/07/08/your-body-wasnt-
built-to-last-a-lesson-from-human-mortality-rates/).

------
willchang
> Anyone who paid attention during introductory statistics will recognize that
> your probability of survival to age t would follow a Poisson distribution,
> which means exponential decay (and not super-exponential decay).

Small correction: survival to time t under the lightning bolt scenario follows
an exponential distribution. A Poisson distribution, besides for being
discrete, has factorial decay, not exponential decay.

------
angdis
The longevity of the body is one thing, it is debatable whether or not it can
be extended by a lot or a little (or at perhaps until the MTBF of a freak
accident).

What I rarely see discussion of, however, are philosophical and psychological
implications of "living indefinitely".

Even if the body is says relatively youthful, what about diseases of the mind?
In other words, I am saying that in the same way that increasing life-span has
uncovered a plethora of diseases that were previously unknown like cancer, is
it possible that further increasing life span may uncover conditions (perhaps
purely psychological) that we can't even imagine. Will people _want_ to live
100's of years?

~~~
JoshTriplett
To the extent we find bugs that cause the brain to stop working properly over
time, we'll need to find and fix those. That falls under "problems we'd love
to have".

As for the question of whether people want to live for hundreds of years: if
you don't want to live longer, you can easily stop. A surprisingly large
number of people seem to rationalize the lack of immortality by claiming
people won't want to live forever, which strikes me as sour grapes. Given an
actual solution that allows people to live forever, the question becomes "do
you want to die?", and I seriously doubt many people will say "yes".

(Also, if you think of immortality as "hundreds of years", I think you need to
recalibrate your scale. I'd like a lifetime measured on a cosmological time
scale, and I have no problem conceiving of ways to spend that time.)

~~~
jonp
As someone who does have difficulty conceiving of ways to spend a
cosmological-scale lifespan, how might you spend it?

~~~
JoshTriplett
Mostly, I'd never stop learning, and I'd apply everything I learned.

Consider the sum total of human knowledge today. Consider how small a fraction
of it any one person knows.

Within the next month, I'll have completed a PhD in computer science. It took
me years to learn the fundamentals of _one_ field, plus years more to get
practical experience by tinkering in numerous areas, plus years more to become
an expert in one narrow area (scalable concurrent data structures) and advance
the state of the art in that area. Take a look at
<http://matt.might.net/articles/phd-school-in-pictures/> to get a clearer
picture of scale; now consider what a few million or billion lifetimes could
produce, between research, practical work, exploration, and just good old-
fashioned tinkering.

How many of those narrow areas exist in one field alone? How many more fields
exist to explore? How many more will exist by that point? What happens when
someone with expert-level knowledge in a pile of those fields starts applying
them to each other? And most importantly, do you really think it ever stops?

Apart from that, I'd have plenty of time between learning everything and
creating new things to enjoy the enormous amount of available entertainment
created over the aeons, in all its various forms.

I think the future sounds awesome, and I want to see _all_ of it. :)

------
drumdance
My dad used to joke that if he made it to 80 he was going to take up smoking
again. Alas, he only made it to 79.

~~~
libraryatnight
A friend used to say that most things he was warned about started with "Men
over the age of 35..." and so once he hit 35 he would stop smoking, drinking,
eating horribly etc. We would usually discuss such things on a smokey patio
with beers.

He's just shy of 35 now, so we'll see ;) Sounds like your dad had a good sense
of humor :)

------
jessriedel
The chance-of-death plots should be logarithmic, so we can tell if this
exponential is really a good fit. On linear plots, it's hard to distinguish
exponential decays from 1/x^n decays.

------
kingkawn
That graph showing survival probability as near 1 for age 0 can't be correct,
since mortality is significantly higher in birth and immediately after, then
drops for a long time, then shoots up again in old age. This is at least true
in westernized countries that have medical care available.

~~~
ArchD
Obviously, this is a simplification. Infants die for other reasons that you
can think of to be different from the reasons for which old people die (e.g.
cancer), and these reasons are being factored out of the graph.

~~~
ryusage
I thought the point of the graph was that it didn't matter how or why the
people died though? Isn't that part of why it's so surprising?

~~~
yelsgib
The point of the graph is that it doesn't matter how or why people die, after
a certain age. This is clear from context, though not explicitly stated.

------
fragsworth
Evolutionary theory would also suggest that we have some mechanism to ensure
our deaths. Longer lifespans cause fewer generations per time period,
resulting in less adaptability as a species.

~~~
JoachimSchipper
Why would evolution need that? If grandpa is badly adapted, he'll starve/get
eaten/etc; no need for a built-in kill switch. In fact, if there were a kill
switch getting rid of it would be highly adaptive, if only because you could
be around to defend your great-grandchildren.

(Of course, we do die. But the explanation looks more like "growing and
reproducing quicker beats longevity" than like "planned obsolescence".)

~~~
JoeAltmaier
Grandpa wears out, yet competes for resources. Kill him off, more for the
healthy youngsters. Certainly its selective, at the family/community level,
choosing to keep more-efficient members.

I also think, making grandparents less mobile means they are around the
campfire teaching the youngsters. It makes sense it would be selected for in a
race of communicators.

~~~
onemoreact
Mice and rabbits also age.

~~~
JoeAltmaier
Sure. But rats quickly die when they become less mobile or arthritic.

Humans can live for decades beyond their most-productive years. Their has to
be a Darwinist reason for this.

~~~
onemoreact
The Darwinist reasoning behind rates of aging goes something like this. A
adult mouse has a high chance of being killed in a random year (above 20%) a
Parrot has a low chance (below 3%). Maintaining a body into old age has a cost
that reduces reproductive capability in a given year and a benefit of
increasing the number of years of reproductive capability. There are also
minimums of capability in the wild where vision and mobility link to survival
rates such that there are thresholds below which rates of survival
dramatically decrease.

Thus, the number of healthy years in the wild relates to both the probability
of an external death AND internal heath issues. For a mouse this suggests a
minimum of internal maintenance for maximum reproduction where a parrot can
make significant trade-offs in reproduction in order to live 10x as long and
have more long term reproductive chances.

 _However_ , that's in the natural setting. A pet (mouse, cat, parrot) can
live slightly longer in captivity by surviving pat the point where it can find
food for it's self. If you look a human vision decline people are
significantly less capable of surviving on their own before they lose
reproductive capability. And in that "unnatural" old age it's not uncommon for
various species to have increasing reproductive issues.

------
ggwicz
One of the sharpest changes (I guess a "point of inflection" it looks like?)
seems to be at about 65, or the most common retirement age (here in the states
at least). I wonder if there's a connection?

In hunter-gatherer societies, elders older than 60 have been observed as 1)
looking healthy and 2) still being able to hunt, fish, trap, build, and pretty
much everything else along with their younger counterparts. Perhaps at a
slower pace, but they're generally far more fit than the modern world's old.

 _Pampered bodies grow sluggish through sloth, movement and their own weight
exhausts them._ \- Seneca

~~~
kiba
_In hunter-gatherer societies, elders older than 60 have been observed as 1)
looking healthy and 2) still being able to hunt, fish, trap, build, and pretty
much everything else along with their younger counterparts. Perhaps at a
slower pace, but they're generally far more fit than the modern world's old._

Survivorship bias.

------
j_baker
Silly question: If I'm understanding this correctly, doesn't this essentially
mean that statistically it's possible to live forever? Or is there a point
when you statistically have 100% probability of dying?

~~~
jbri
Sort of, depending on the model. For most models, if you take your
"probability of dying in year X", and sum that over all the years from 0 to
infinity, you'll get a 100% probability of dying at some point. The
interesting thing is that there's no individual year with a 100% probability
of dying - the certainty of death is just because "forever" is a _really long
time_.

There are hypothetical distributions, though, where the sum total of
probabilities is less than 100% - where some proportion of the population
will, statistically, never die.

Of course this brings us to the _real_ issue, which is that what the model
says doesn't really matter - if the model disagrees with reality in extreme
cases, reality wins.

~~~
usaar333
On high ends it definitely is. It predicts no one could have ever lived past
116, but clearly some have:

<http://en.wikipedia.org/wiki/Oldest_people>

------
ifearthenight
Fun and interesting read. Personally though I think by only examining
mortality rates then half the story has been missed. ie. life expectancy.

While intuitively we can see that the probability of dying in any given year
increases with the more years you live, perhaps slightly more counter
intuitively the longer you live then the longer your life expectancy is
(rolling average obviously).

Would love to see the two put together somehow and charted.

------
scotty79
Are there any other scenarios that lead to Gompertz Law like distribution?

