Re: Digital Genetics and Evolution Theory

Bioteach wrote:
Perplexed wrote:

The idea that senescence and death exist in sexual organisms for the
*purpose* of allowing the variant young to compete among themselves
(without the older generation siphoning off all of the resources) is
hardly an original one. I've seen enough modeling to convince me that
this may be part of the story, but it is not the full story. The
other part is the sheer difficulty of keeping large complex organisms
from simply wearing out. Some plants (trees, mostly) are designed so
that new generations of tissue can make productive use of the older,
worn-out generations of tissue. Animals (and especially animal
central nervous systems) just can't work that way.

Although everybody recognizes that there is wear or other unrepairable
damage that could accumulate in an organism, it seems to be pretty clear
that wear cannot be the main explanation for observed life span
characteristics. This is because very similar organisms with very
similar cell biology have grossly different life spans. (e.g. mouse and
human, crow and parrot, many other examples)

The idea is that lifespan characteristics can be explained
primarily by selection on repair and maintenance mechanisms.

Relatively short-lived creatures allocate more resources to
short-term reproduction at the expense of repair and
maintenance mechanisms. Those that live longer allocate more
resources to repair and maintenance - perhaps because growth
is resource limited, because they have a more plastic
developmental process, or because they provide more parental
care.

There are also organisms possessing biological suicide mechanisms
that clearly are not accumulative (e.g. bamboo, octopus).

Can you be more specific? There are plenty of causes of
death that are not cumulative - but they need not be
suicidal.

Also, suicide is actually /expected/ in some plants - where
the parents live near the offspring, compete for resources
with them, or act as a parasite reservoir that could
infect them.

In such cases, individual death can be adaptively favoured
by kin selection.

Finally, there are organisms that do not have any measurable aging
(e.g. Pacific rockfish) even at 150 years old when similar organisms
have much shorter life spans.

I am not sure how negligible senescence bears on the issues of
group selection or adaptive death. An organism with negligible
senescence simply has good repair and maintenance mechanisms.

Indeed, one might ask, if senescence is supposedly adaptively
favoured, why these organisms do not exhibit it.

The currently most respected "main line" aging theories ignore group
selection, adhere to Darwinian theory, and propose that aging is an
unavoidable adverse side-effect of some beneficial function. If you
assume the beneficial function is reproduction related, this then fits
better with the observations than wear. However, the book describes
what appear to be several major logical flaws in the main line theories.

?

FROM Tyler:

The idea that variation-producing characteristics were able to
evolve despite fitness disadvantage because they convey an
improvement in the capacity for evolution - is widely regarded
as not the correct explanation.

In fact there are other, more direct short-term fitness advantages
to diversity-producing traits - such as sexual recombination.

That this is the case can be seen by consideration of organisms
that exhibit facultative parthenogenesis. These organisms can
clone themselves - but often choose not to do so.

Similarly, the idea that variation considered as an evolved design
feature is itself incompatible with Darwinian evolution is
equally incorrect :-(

In fact, clones are often regarded unfavourably by natural
selection - primarily since groups of genetically identical
organisms can easily be exploited by pathogens.

There are other defenses against pathogens besides adapatations that
promote diversity: immune systems, being rare, and very rapid
dispersal, with no parental care.

Immune systems allow some of the advantages of cloning without using
diversity as a defense. However the strategy is typically only
effective in the short term.

Diversity is a simple and reasonably effective defense against
pathogens - it is not surprising to find adaptations that promote it.

This is an argument for how one of the discrepancies (variation
producing features) might be resolved without violating orthodox
Darwinism and embracing some form of group selection. It seems somewhat
implausible that sexual reproduction and all the other complexity
evolved just for this one function, but possible. (Wouldn't there have
been an easier way?)

It is not the hypothesis that parasites are /solely/
responsible for the origin and maintenance of sexual
recombination. There is at least one other important theory of
the origin and maintenance of sex: the gene repair theory.
Sex weeds out deleterious mutations by concentrating them in
single bodies, and which then die or fail to reproduce.
However, pressure from parasites is an important reason for
the continued existence of sexuality - and explains much of
its ecological variation.

Sex may seem like a bizarre anti-parasite adaptation, but the
answer to the question of whether there was an easier way
appears to be 'no'.

Life /may/ find other ways of coping with parasites in the
future. It may generate diversity by other means than sexual
recombination, and it may combat pathogens directly, with
medical technology, and a global immune system. If these
approaches to eliminating pathogens are successful, a
question mark may appear over the utility of sexual
reproduction in nature.

However, so far human attempts at pathogen control have been
pretty feeble. Viruses and worms cause billions of dollars of
loss in artificial ecosystems created by humans - in computer
networks. Modern computer systems couldn't be more insecure
if the NSA had designed them itself.

If human beings are really /this/ incompetent or indifferent
to pathogens, perhaps there is little hope of progress in
combating them.

Still, I attrubute the current screw-up to copyright law - which
has created a near monopoly one area. The monopolist has
proved themselves either incompetent or failing to have the
best interests of the people at heart - resulting in the current
pathogen problem.

IMO, there are signs that this type of management screw-up will
have a limited lifespan under the current political system -
too many voters want their MP3s decriminalised, and - according
to current political thought - their wishes outweigh those of
the mega corporations, who want to continue to screw them out
of their dollars.
--
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|im |yler http://timtyler.org/ tim@xxxxxxxxxxx Remove lock to reply.


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