On Sun, 9 Jul 2000, Damien Broderick wrote:
> An interesting post, which led me to consider an issue I've never seen
> discussed in the literature (although this is doubtless due to my
> ignorance): selective differentials from secular variations in sunlight,
> temperature etc and their impact on creatures with variant breeding and
> mortality patterns.
I suspect that the long term variations are effectively "noise" compared
with short term variations driven by the chaos in the system. The
energy differentials from the sun are probably small compared with
the local effects of tornadoes, hurricanes, earthquakes, volcanoes, etc.
Energy input significantly effects breeding ability. Environmental
hazards are the determinants of the hazard function that drives the
engineering of greater or lesser "anti-aging" genetic programs.
>
> If this has any bearing upon which phenotypes are best adapted at any given
> slice across the cycles, I can imagine that critters which store food might
> tend to live longer than those which don't;
Rose's long-lived flies have a characteristic of having greater fat reserves.
This allows them to live longer after their mouth/feeding parts wear out.
You can imagine that prehistoric humans suffered nutritional deficiencies
after they lost all their teeth that would contribute to decreased longevity.
Elephants die because their teeth wear out.
However -- it is difficult for me to connect these things with long-term
climate cycles.
> long-distance north-south migratory beasties might live longer than others
> of the same metabolic indices;
Birds live longer because they have a generally lower hazard function
(very few predators).
> and fish, lobsters or other critters in the stabilised environment
> of the sea might produce some species that escape mortality entirely (as
> Joao was suggesting, I think).
The two species that Kirkwood suggests escape mortality entirely are
sea anenomies and hydra. Sturgeon, Rock fish, lobsters and giant clams
probably all benefit from the stable environment and/or good defenses
that allows nature to evolve their programs towards slowly aging
phenotypes. It is likely to be impossible to get a completely non-aging
phenotype because you cannot grow large enough to produce ever more
offspring to maintain the fraction of "longevity" genes in the
overall species gene pool. Subsets of the species that divert energy
for maintenance and repair into reproduction will eventually
out reproduce those that sacrifice reproduction for repair. This
results in species longevity averages that are shorter than what
could be possible.
Robert
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