"Tim Tyler"  wrote in message
news:c7mqjh$268s$1{at}darwin.ediacara.org...
> Perplexed in Peoria  wrote or quoted:
> > "Tim Tyler"  wrote in message
> > > Jim Menegay  wrote or quoted:
> > > > Tim Tyler  wrote in message
>
> [Species-level developmental programs?]
>
> > > > > What about phylogeronty (species senescence) -
i.e. the "dinosaur"
> > > > > effect - the theory that "old",
well-established species tend to
> > > > > get set in their ways, become a target for attack,
accumulate a
> > > > > load of pathogens - and suffer increased mortality
as a result?
> > > >
> > > > Tim, are you suggesting the existence of a kind of
"programmed
> > > > species death"?  If so, "who" did the
programming?  Or rather,
> > > > what entity at what level enjoys this phenomenon as an
adaptation?
> > >
> > > The most conventional explanations for organism-level senescense are:
> > >
> > > * Disposable soma
> > >
> > >    Reproductive and maintenance processes compete for
> > >    resources. Reproducing early clearly has many advantages -
> > >    and is consequently somatic tissue maintenance programs do
> > >    not receive sufficient investment to support indefinite
> > >    survival.
> > >
> > > * Antagonistic pleiotropy
> > >
> > >    This theory proposes that genes that delay the expression
> > >    of deleterious genes are favoured. More generally, it
> > >    suggests that alleles may be favoured if they have
> > >    beneficial early effects but deleterious later effects.
> > >
> > > Neither theory suggests death is adaptive.  [snip]
> >
> > If the examples you are offering of "species development" are not
> > adaptive, then you should not call the phenomena "development".
> > It just creates confusion.  Call them "common patterns in species
> > evolution" or something.  Biologists have been trained to think
> > of "programming" when they see the word
"development" and
> > they have been trained to think of that programming as adaptive.
>
> The disposable theory *is* an adaptive theory.
>
> ...but senescence is not the "aim" of the adaptation involved.
>
> The adaptation involves diverting resources away from maintenance
> programs and into reproductive activities.
>
> Aging is a side effect of this adaptation - not its goal.
>
> The result is very clearly a developmental program - by everyone's
> definition of the term.
>
> Biologists are quite happy referring to the effects of
> the "disposable theory" as a developmental program.  The result
> is a "built-in" series of life stages starting with birth and
> culminating with death - clearly development.
>
> To ask who death benefits is the wrong question, though.
>
> For example, with conventional antagonistic pleiotropy, one of the
> causes of death is selection favouring delayed expression of
> deleterious genes.  In those cases, if you could surgically
> rip out the deleterious genes in question (rather than merely
> delay their expression) you would likely wind up with individuals
> with longer reproductive lifespans and greater fitnesses - i.e.
> in those cases, death is likely to be maladaptive.
>
> Death doesn't *have* to benefit anyone to exist.  It can be a side
> effect of something else which *is* beneficial.
>
> If you are suggesting side effects of adaptations are not recognised
> by biologists as contributing to development - then I suggest that's
> baloney:
>
> Side effects of adaptations with other goals (besides creating a
> developmental program) feature prominently in the causation of
> senescence - according to conventional theories of aging.

Confusion has arisen here and it may have been my fault - I was
careless in which parts of your reply I clipped, and which parts I
retained.

I did not argue that *organism level* senescence is not an adaptation.
I am in full agreement with the conventional wisdom within biology
which claims that it is certainly not maladaptive and may sometimes
be positively adaptive.

What I was arguing is that *species-level* senescence is not adaptive
(if it even exists) and therefore should not be considered as part of
a "development program".

Please, Tim, don't respond to the "if it even exists".  I have heard your
arguments on that before.  Please respond to the question as to
whether it should be described as part of a species development
program if it does exist.
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