Josh Mitteldorf - Evolution and CR
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What CR tells us about evolution - Death is by design - aging is a metabolic
program under genetic control, and presumably is there because it evolved as
an adaptation.

So why doesn't body do the same thing (adaptation) when food is plentiful?
If aging is an active process, why do we do it?

What does evolution have to tell us about life extension?  Natural is out -
high tech is in. What does this mean - If you give us a natural diet (normal
amount of food), that isn't best for us.  If aging is a programmed process,
rather than just a matter of decay - then there is the potential that
targeted technology could intervene effectively with the process.

What is adaptive value of CR from an evolutionary perspective? Answer:
Evolutionary cost of aging going to be higher in period of famine than in
period of plenty. If you can hang on during famine, then when you make it
through, you'll see less competition because others have died. CR allows you
to seed the new population once famine subsides, and your offspring to
survive and therefore pass on your genes.

So why doesn't the body do this all the time? I.e. maintain its systems
better? Traditional answer - necessary tradeoff between fertility and
longevity. Balance between having children now when there is a famine,
compared with putting resources into surviving longer so that you can bear
children after famine is over. In times of plenty, better to devote
resources to reproduce fast and furiously, rather than "hunkering down"
through CR adaptations towards maintainence and away from reproduction.

In nature, few animals die of old age. But not the same thing as aging
having no effect. If you become 5% less capable due to aging (slower, less
strong), you'll be outcompeted by younger animals, and will therefore die
out.

By shortening lifespan, and forcing younger reproduction, aging could
increase population turnover, and accelerate the rate of evolution, so get
good changes in genes to happen more quickly. Doesn't work quantitivily.

Problem with other explanation - limited resources to devote to fertility or
maintainence/repair, but not both. Kirkwood's Disposable Soma theory.
Problem is that the "resources" that are supposedly limited is food energy,
which isn't limited during times of plenty.

Genetic tradeoff hypothesis. Genes necessary for effective reproduction may
be deleterious to longevity. Flies that are breed over many generations for
longevity have increased, not decreased fertility in the lab. So maybe no
tradeoff. But in the lab, reproductive fitness isn't rewarded, only
fertility.

Josh's new theory of where does aging come from. The answer "population
homeostasis". In the wild, it seems clear that boom and bust cycles in
population are very common. When food is plentiful, populations reproduce
very quickly (boom), and make too many offspring which eat all the food and
die off when they grow up (bust). To avoid this, and stabilize population,
animals regulate their own population, through aging.

Example: Lion and gazelle are competing in the wild for speed. If lions are
too slow, they'll die off from starvation. But if they are too fast, they'll
die out as well, because they'll do very well at catching gazelles, and
reproduce more, and all the lions will eat up all the gazelles, so the lions
will starve, crashing their population.

Aging solves this problem. As the young gazelles get old, they slow down and
provide a steady stream of food for the lions. So lion population won't boom
or bust. This helps keep population of predator and prey stable.