T
Tim Tyler
Guest
Here's my "Universal senescence" essay.
It can be found on the web - at:
--> http://alife.co.uk/misc/universal_senescence/ <--
To offer a brief synopsis:
I suggest that the tendency of many sorts of object to fall
to bits represents a general rule of complex systems.
This rule is distinct from the second law of
thermodynamics, and - unlike the second law - can be
applied to open systems.
The aging of biological organisms represents a particular
instance of this rule.
I think the idea is a pretty obvious one - and I'd be
suprised if it originated with me. Any references to prior
work would be gratefully received.
Universal senescence
====================
An increasing tendency to fall to bits
--------------------------------------
A naive interpretation of the second law of thermodynamics
describes it as an increasing tendency of things to fall to
bits as time passes.
This isn't what the second law /actually/ says - but the
idea /does/ have a sort of intuitive appeal - since it
/does/ seem that many common objects /do/ eventually
fall to bits.
Could it be that this tendency deserves to be described as a
universal aspect of complex systems?
Occasional disintegration
-------------------------
Complex adaptive systems follow lawful behaviour just like
other objects do - though in many cases the rules they
follow may not yet be entirely clear.
These laws are best regarded as /additional/ rules of
thermodynamics designed to deal with complex adaptive
systems.
By far the most obvious rule is the statment of how such
systems affect entropy - which I have previously attempted
to describe [snip reference to my "bright light" essay].
Here I would like to propose that the phenomenon of
senescence is a common feature of a range of complex
adaptive systems - and can be characterised by the
occasional disintegration of such systems.
The suggested rule is different from the second law of
thermodynamics. That also suggests that complex systems tend
to fall to bits - but it can only be used to make that
prediction in closed environments.
The proposed rule does not have that restriction - the
intention is that it can also be applied to self-organising
systems in open environments.
Subjects of senescence
----------------------
Probably the most familiar senescing objects are biological
organisms.
Senescence is common in biology, and - among more complex
organisms - it is / nearly/ universal.
However, other sorts of system also exhibit senescence.
In particular, complex pieces of machinery also exhibit
limited lifespans - and often have lifespan curves
suggesting that progressive degradation followed by
catastrophic collapse is occurring - the signature of
senescence.
To gives some concrete examples, I claim this is true of
cars, houses, computers, stereos, clocks, motors, hyraulics
and companies.
Causes of senescence
--------------------
Why do complex things tend to fall to bits?
It appears that there are many reasons - and that different
ones can apply to different sorts of system:
- *Environmental damage* - complex systems are exposed
to damage from their environment. Often no individual
bit of damage it worth repairing - but the cumulative
long-term effects of the damage is that the system
degrades over time
- and eventually stops functioning.
- *High repair costs* - complex systems are often
difficult to repair. They can need specialist knowledge
to locate the problem and specialised tools to fix it.
This can mean that some problems are more cheaply fixed
with a new model.
- *High cost of durable components* - one simple strategy
aimed at preventing things from falling to bits is to
build them out of strong, durable materials.
Unfortunately, these are often expensive and difficult
to machine.
- *Planned senescense* - some things fall to bits simply
because they were / designed/ to fall to bits. A broken
piece of machinery often creates demand for a replacement.
Sometimes, there is little incentive for manufacturers to
build long-lived components - since doing so destroys
their future market.
- *Disposable soma* - reproductive and maintenance processes
can compete for resources. Reproducing early has many
advantages - and is consequently somatic tissue
maintenance programs do not receive sufficient investment
to support indefinite survival.
- *Antagonistic pleiotropy* - this is the idea that genes
that /delay/ the expression of other deleterious genes
are favoured.
More generally, it suggests that genes may be favoured
if they have beneficial early effects but deleterious
later effects.
- *Cumulative parasite load* - systems accumulate parasites
faster than they succeed in ridding themselves of them.
The result is progressive loss of function - followed by
catastrophic collapse.
- *Obsolescence* - in a rapidly changing environment systems
may be discarded because they are out of date. This effect
is commonly seen in computer systems - but also arises
among organisms who are in combat with parasites which
evolve to adapt to common host genotypes - where older
genotypes are more likely to encounter parasites that have
evolved the capability of exploiting their resources.
The role of complexity
----------------------
Complex systems are often more expensive to replace than
corresponding simpler ones. This makes replacing them more
expensive.
However, they also have more different bits to go wrong. It
is harder to identify the cause of problems - and it
typically require an engineer with more spare parts and
specialised knowledge to fix.
The case of companies
---------------------
The theory of "universal senescence" suggests that companies
exhibit senescence.
However - as far as I am aware - this theory has never
been tested.
It should not be too difficult to test - and the results may
be of some interest.
In theory, a number of mechanisms of senescence ought to
apply to companies.
In particular, companies:
- ...are vulnerable to environmental damage;
- ...can grow large, become unable to manoeuvre properly -
and then crash;
- can accumulate garbage in their components in the form of
well-disguised dud employees or poorly-designed systems -
in a way that makes the problem difficult to repair;
- ...can reach a size where they become attractive to
predators - and vulnerable to being swallowed up and
destructively digested - in a merger with a larger
company;
- ...that have been around longer have increased chances of
attracting parasites - either agents inside the company
who do not have its best interests at heart or externally-
run protection rackets - and the like.
Companies are an interesting case - since most companies are
still very young - and have not directly descended from
other senescing companies. Thus - unlike most complex
organisms with substantial genomes - they are not "built to
senesce". However the theory suggests that they will -
nontheless - exhibit senescence - and that the effect will
/probably/ be big enough and visible enough to be evident
from their lifespan curves.
Unfortunately, companies /also/ exhibit the equivalent of
"large infant mortality" - and the effect is a substantial
one. This may act to obscure the effect of senescence over
the lifespan of the majority of companies.
This may make company senescence more difficult to detect.
Modularity
----------
Can senescence be defended against using modularity? It
seems that - by using a modular design and "unit tests" that
failures in individual modules can be identified, isolated
and repaired - without large-scale failures necessarily
being involved.
Modularity is - without doubt - a major weapon aganist
senescence.
However there are a few drawbacks:
- Modularity is a design constraint that conflicts with
efficiency. This is probably why (for example) we don't
have twelve hearts - one heart simply works better;
- Unit tests - and the time spent executing them - also
represent something of a burden;
Also, modularity doesn't /completely/ fix the problem. There
is still the issue of connections between the modules. These
themselves senesce - and may not be so easy to diagnose
problems in.
There are also the possibilty of unplanned-for failure
scenarios within modules - failures that cause unit tests
to mis-report, failures that knock out whole modules -
and so on.
Exceptions
----------
There are a few complex organisms that don't senesce. How do
those fit into the idea of "universal senescence"?
Not very well, it must be said. However, they are not very
common - and the theory doesn't suggest that /all/ long-
lived organisms must senesce - it merely provides reasons
why most of them might.
One way to ensure you have good repair mechanisms is to make
sure finding a mate and reproducing is very, very difficult
- so that it can take a very, very long time.
Under such circumstances, selection will favour very long
lifespans.
I am happy to agree that selection is powerful enough to
produce organisms with extremely long lifespans. However I
am inclined to doubt whether that sort of selection will
ever be acting very frequently.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove
lock to reply.
It can be found on the web - at:
--> http://alife.co.uk/misc/universal_senescence/ <--
To offer a brief synopsis:
I suggest that the tendency of many sorts of object to fall
to bits represents a general rule of complex systems.
This rule is distinct from the second law of
thermodynamics, and - unlike the second law - can be
applied to open systems.
The aging of biological organisms represents a particular
instance of this rule.
I think the idea is a pretty obvious one - and I'd be
suprised if it originated with me. Any references to prior
work would be gratefully received.
Universal senescence
====================
An increasing tendency to fall to bits
--------------------------------------
A naive interpretation of the second law of thermodynamics
describes it as an increasing tendency of things to fall to
bits as time passes.
This isn't what the second law /actually/ says - but the
idea /does/ have a sort of intuitive appeal - since it
/does/ seem that many common objects /do/ eventually
fall to bits.
Could it be that this tendency deserves to be described as a
universal aspect of complex systems?
Occasional disintegration
-------------------------
Complex adaptive systems follow lawful behaviour just like
other objects do - though in many cases the rules they
follow may not yet be entirely clear.
These laws are best regarded as /additional/ rules of
thermodynamics designed to deal with complex adaptive
systems.
By far the most obvious rule is the statment of how such
systems affect entropy - which I have previously attempted
to describe [snip reference to my "bright light" essay].
Here I would like to propose that the phenomenon of
senescence is a common feature of a range of complex
adaptive systems - and can be characterised by the
occasional disintegration of such systems.
The suggested rule is different from the second law of
thermodynamics. That also suggests that complex systems tend
to fall to bits - but it can only be used to make that
prediction in closed environments.
The proposed rule does not have that restriction - the
intention is that it can also be applied to self-organising
systems in open environments.
Subjects of senescence
----------------------
Probably the most familiar senescing objects are biological
organisms.
Senescence is common in biology, and - among more complex
organisms - it is / nearly/ universal.
However, other sorts of system also exhibit senescence.
In particular, complex pieces of machinery also exhibit
limited lifespans - and often have lifespan curves
suggesting that progressive degradation followed by
catastrophic collapse is occurring - the signature of
senescence.
To gives some concrete examples, I claim this is true of
cars, houses, computers, stereos, clocks, motors, hyraulics
and companies.
Causes of senescence
--------------------
Why do complex things tend to fall to bits?
It appears that there are many reasons - and that different
ones can apply to different sorts of system:
- *Environmental damage* - complex systems are exposed
to damage from their environment. Often no individual
bit of damage it worth repairing - but the cumulative
long-term effects of the damage is that the system
degrades over time
- and eventually stops functioning.
- *High repair costs* - complex systems are often
difficult to repair. They can need specialist knowledge
to locate the problem and specialised tools to fix it.
This can mean that some problems are more cheaply fixed
with a new model.
- *High cost of durable components* - one simple strategy
aimed at preventing things from falling to bits is to
build them out of strong, durable materials.
Unfortunately, these are often expensive and difficult
to machine.
- *Planned senescense* - some things fall to bits simply
because they were / designed/ to fall to bits. A broken
piece of machinery often creates demand for a replacement.
Sometimes, there is little incentive for manufacturers to
build long-lived components - since doing so destroys
their future market.
- *Disposable soma* - reproductive and maintenance processes
can compete for resources. Reproducing early has many
advantages - and is consequently somatic tissue
maintenance programs do not receive sufficient investment
to support indefinite survival.
- *Antagonistic pleiotropy* - this is the idea that genes
that /delay/ the expression of other deleterious genes
are favoured.
More generally, it suggests that genes may be favoured
if they have beneficial early effects but deleterious
later effects.
- *Cumulative parasite load* - systems accumulate parasites
faster than they succeed in ridding themselves of them.
The result is progressive loss of function - followed by
catastrophic collapse.
- *Obsolescence* - in a rapidly changing environment systems
may be discarded because they are out of date. This effect
is commonly seen in computer systems - but also arises
among organisms who are in combat with parasites which
evolve to adapt to common host genotypes - where older
genotypes are more likely to encounter parasites that have
evolved the capability of exploiting their resources.
The role of complexity
----------------------
Complex systems are often more expensive to replace than
corresponding simpler ones. This makes replacing them more
expensive.
However, they also have more different bits to go wrong. It
is harder to identify the cause of problems - and it
typically require an engineer with more spare parts and
specialised knowledge to fix.
The case of companies
---------------------
The theory of "universal senescence" suggests that companies
exhibit senescence.
However - as far as I am aware - this theory has never
been tested.
It should not be too difficult to test - and the results may
be of some interest.
In theory, a number of mechanisms of senescence ought to
apply to companies.
In particular, companies:
- ...are vulnerable to environmental damage;
- ...can grow large, become unable to manoeuvre properly -
and then crash;
- can accumulate garbage in their components in the form of
well-disguised dud employees or poorly-designed systems -
in a way that makes the problem difficult to repair;
- ...can reach a size where they become attractive to
predators - and vulnerable to being swallowed up and
destructively digested - in a merger with a larger
company;
- ...that have been around longer have increased chances of
attracting parasites - either agents inside the company
who do not have its best interests at heart or externally-
run protection rackets - and the like.
Companies are an interesting case - since most companies are
still very young - and have not directly descended from
other senescing companies. Thus - unlike most complex
organisms with substantial genomes - they are not "built to
senesce". However the theory suggests that they will -
nontheless - exhibit senescence - and that the effect will
/probably/ be big enough and visible enough to be evident
from their lifespan curves.
Unfortunately, companies /also/ exhibit the equivalent of
"large infant mortality" - and the effect is a substantial
one. This may act to obscure the effect of senescence over
the lifespan of the majority of companies.
This may make company senescence more difficult to detect.
Modularity
----------
Can senescence be defended against using modularity? It
seems that - by using a modular design and "unit tests" that
failures in individual modules can be identified, isolated
and repaired - without large-scale failures necessarily
being involved.
Modularity is - without doubt - a major weapon aganist
senescence.
However there are a few drawbacks:
- Modularity is a design constraint that conflicts with
efficiency. This is probably why (for example) we don't
have twelve hearts - one heart simply works better;
- Unit tests - and the time spent executing them - also
represent something of a burden;
Also, modularity doesn't /completely/ fix the problem. There
is still the issue of connections between the modules. These
themselves senesce - and may not be so easy to diagnose
problems in.
There are also the possibilty of unplanned-for failure
scenarios within modules - failures that cause unit tests
to mis-report, failures that knock out whole modules -
and so on.
Exceptions
----------
There are a few complex organisms that don't senesce. How do
those fit into the idea of "universal senescence"?
Not very well, it must be said. However, they are not very
common - and the theory doesn't suggest that /all/ long-
lived organisms must senesce - it merely provides reasons
why most of them might.
One way to ensure you have good repair mechanisms is to make
sure finding a mate and reproducing is very, very difficult
- so that it can take a very, very long time.
Under such circumstances, selection will favour very long
lifespans.
I am happy to agree that selection is powerful enough to
produce organisms with extremely long lifespans. However I
am inclined to doubt whether that sort of selection will
ever be acting very frequently.
--
__________
|im |yler http://timtyler.org/ [email protected] Remove
lock to reply.