Re: The ultimate cause of aging


dkomo <dkomo871@xxxxxxxxxxx> wrote:-

"The basic reason why survival and reproduction decline with age is that
selection acts more weakly on later ages. Imagine an organism that does
not senesce, that is, that maintains itself with the same rate of
survival and reproduction indefinitely. It will still suffer accidental
mortality and so, on average, reproducing early will produce more
offspring than deferring reproduction until later; death might strike
first.

JE:-
I have been arguing this within sbe for about 10 years. The net result is
that survival cannot be a fitness maximand.

Therefore, natural selection acts more strongly on variations
that act early in life and acts more and more weakly on late-acting
acting variations (see Box 20.2).

JE:-
Natural selection must act to maximise fitness, no matter how fitness
happens to be defined. Since only fertile forms can possibly pass on their
genes, selection _for _ can only act on later developed fertile forms.
Therefore selection operates less strongly "on variations that act early in
life" and can only act fully after all immature forms have been raised to
fertile adulthood. Selection against (not for) these forms acts if they die
before they could be raised to fertile adulthood. This provides each
selectee with just the ONE Total Darwinian Fitness (TDF) as a falsifiable
fitness maximand per population. TDF is defined as: the total number of
strictly fertile forms raised to adulthood per parent per population. If two
or more maximands are provided per selectee per population (as polycentric
Neo Darwinism allows) then they must contest until only one survives OR they
fitness mutualize as entirely independent fitnesses, i.e. at least two
independent selectees must now be hypothesised.

If, as a result, senescence starts to
evolve, then there will be a feedback, so that selection on later ages
becomes even weaker. In the extreme case, where an organism such as a
salmon reproduces only once, there is absolutely no selection on
subsequent survival."

Nicholas Barton et al, _Evolution_, p. 562

JE:-
The human gap between giving birth and raising babies to fertile adulthood
is about 15 years. This would mean that a woman at menopause would be
selected to have at least another 15 years to complete the job allowing her
to live to 50+15 =65. She may be selected to live longer if she provides a
mutualised fitness benefit by doing do. An example would be that older
people become the repository of tribally based knowledge.

As an example, suppose our physiologically immortal animal is called the
shmoo, and it has a death rate of 10% per year due to environmental
causes such as predation, lack of food or water, parasites, diseases,
heat, cold, floods, severe snowstorms, or accidents such as falling into
swiftly moving rivers or from cliffs. That means that the average
schmoo has only a 35% chance of living past the age of 10, and a 12%
chance of living past 20. Suppose further that once a shmoo reaches
maturity at the age of 5, it reproduces each year with undiminished
vigor until it dies.

JE:-
Yes, it is entirely possible to argue that reproduction and death can evolve
a fixed survival rate. The most famous example are salmon. They are selected
to die by their own hand after spawning entirely within the ecosystem in
which they have given birth because this will increase and not decrease the
chance of raising more of their own infertiles to fertile adulthood.
Attempting to swim away and do it all over again mostly resulted in the
parents dying somewhere else, donating their bodies to a foreign ecosystem.
It seems to me that ecosystem concept hinges on mutualised fitnesses acting
across the ecosystem. Without any TDF understanding it remains impossible to
produce a mutualised fitness concept because no frame of reference exists to
allow it. This is why I keep on stressing that Hamiltonian altruism is not
at all real. Inclusive fitness has no constant frame of reference so it is
only a mathematical, i.e. not at all a scientific argument.

snip<

Regards,

John Edser
Independent Researcher

edser@xxxxxxxxxxxxxx


.

Relevant Pages

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