Re: Digital Genetics and Evolution Theory

Tim Tyler <seemysig@xxxxxxxxxxxxxx> wrote in
news:eqqfs8$dql$1@xxxxxxxxxxxxxxxxxxx:

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.

Bamboo evidently reproduce by essentially cloning, like grass.
Occasionally they flower and seed. When they flower, they die. Death
is programmed to accompany blooming and clearly not a maintenance issue.
Programmed death is apparently to prevent cloning from dominating sexual
reproduction.

Octopi females stop eating after reproduction and die of self
starvation. Some Polish biologist whose name I do not remember
determined that surgically removing the eyes eliminates this behavior.
No obvious way to make this into a maintenance issue.

Salmon die of old age after mating.





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.

Yes the very few organisms that do not appear to age could have really
good repair mechanisms (maintenance, Darwinian, aging is not a benefit
view) or could have lost their ability to age (aging is an evolved
beneficial feature, group selection view). The existence of negligible
senescence doesn't prove anything one way or another, except that SOME
organisms have apparently escaped aging and that it is therefore
possible.

I think there are bigger problems with the maintenance theories:


If an organism can build itself from essentially nothing, how come
repair is such a problem? Replacing a cell shouldn't be very much
different from growing it in the first place. Many cells, (skin, blood)
are replaced often.

Why do things like exercise and other forms of stress seem to extend
life span if maintenance is the issue? This seems the opposite of what
one would expect.





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.
--
__________
|im |yler http://timtyler.org/ tim@xxxxxxxxxxx Remove lock to
|reply.




Those who do not believe in group selection think that the individual
benefits of sexual reproduction (e.g. pathogen resistance) outweigh the
seemingly major individual disadvantages allowing the major complexities
of sexual reproduction to evolve. Those who do believe in group
selection think that the major group benefits (essentially enabling the
evolution process in complex organisms) outweigh the individual
disadvantages. There is no way that either side can prove their case to
the satisfaction of the other.

My limited experience suggests that once formed, beliefs about group
selection are very deeply held. Someone is about as likely to change
their beliefs about group selection as they are likely to change their
religious beliefs.

.

Relevant Pages

  • Re: Mendel refutes evolution
    ... Meiotic drive is just selection. ... I deny the validity of a term like "species selection". ... because it kills of organisms who ... reproduction that has nothing to do with genetic or phenotypic ...
    (talk.origins)
  • Re: The ultimate cause of aging
    ... survival and reproduction indefinitely. ... natural selection acts more strongly on variations ... The basic problem with it, however, is that there is evidence of senescence effector and suppressor genes that control the rate of aging in some organisms. ...
    (talk.origins)
  • Re: Nando Explains Natural Selection to You!
    ... > of natural selection, such as chance, neutral selection, genetic drift. ... phenotype X ... as you would compare variant organisms. ... > are based on the logic that all organisms die, through reproduction the ...
    (talk.origins)
  • Re: Nando Explains Natural Selection to You!
    ... >> are based on the logic that all organisms die, through reproduction the ... But it is *differential reproduction of variant phenotypes* ... > Not if there is no *selection* between variants. ...
    (talk.origins)
  • Re: Sociobacteriology
    ... necessity of germ line segregation in metazoan organisms that I have seen. ... any specific method of reproduction. ... The individual trees grow tall to compete for sunlight. ... I fed Cuban tree frogs to my ribbon snake ...
    (talk.origins)