Quite intriguing, John. Kirkwood's 'disposable soma' theory of aging has been gaining quite a bit of credence lately. It makes sense that the organism has to make a compromise in whether to allocate resources to reproduction vs. maintenance and growth, etc. This Wikipedia article gives some more background:
http://en.wikipedia.org/wiki/Evolution_of_ageing#Disposable_soma_theoryHowever, the article also mentions that it is not easy to reconcile the benefits of caloric restriction with the disposable soma theory:
Actually there's a rather common(and I think very reasonable) argument that fits caloric restriction neatly within the Disposable Soma theory.
The basic argument is that caloric restriction simulates starvation. The forces of evolution ultimately work to enhance the chances of successful reproduction for each species, and starvation, evolutionarily speaking, has been a state that reduces the chances of successful reproduction. Scarce food conditions are generally not beneficial to successfully producing healthy offspring.
Since starvation was probably often periodic and not chronic(due to seasonal food shortages etc), the best bet for successful reproduction is for the organism to temporarily move energy away from reproductive mechanisms and toward survival and repair mechanisms, the hope being that they increase their chances of surviving the starvation period and living until conditions become more conductive for reproduction.
It's also known that caloric restriction can significantly lower fertility levels(when severe, even to the point of some genital atrophy) which matches this theory perfectly too.
Do you see an analogy between bodily impact and caloric restriction as far as how they might affect aging?
I see a lot of commonality between the two. Injury and starvation would likely both have been harmful to the chances of successful reproduction, and in both cases evolution may have created mechanisms which switch the organism toward repair and survival, at the expense of the reproductive system, so that the organism could have a higher chance of reproducing at a later time - when the starvation and/or injury had passed.
It's obvious that evolution has created repair mechanisms for injury, and if we assume that ultimately evolution is all about maximizing reproductive success, then these repair mechanisms are nothing more than attempts to get the organism back into maximal reproductive fitness.
Basically, evolution only cares for the organism itself(such as repairing it and maintaining health) to the degree that caring for it increases reproductive chances. If, on average, an animal will die anyway from external causes(predators, accident, infectious disease) by age 30, then evolution "weighs up the odds" and decides it's only worth engaging in repair and maintenance mechanisms to survive in decent shape until 30 - thus freeing up more energy for reproductive activities.
From this perspective, both caloric restriction and physical trauma/injury may act as a signal to evolutionarily conserved mechanisms which essentially say "I'm in a poor position to reproduce at the moment, the best thing to do would be to stop wasting energy on my reproductive systems and route energy toward repairing myself and surviving until a later date when conditions for reproduction will hopefully be better."
Or, one way I like to see it is "Up yours evolution! I, as an individual, am more important than my ability to reproduce, and I'm going to short-circuit your system and place emphasis on
my survival not my sperms' survival."
