Background for why I am asking this:
I read a book—modern biological theory and experiments on celibacy— which uses life history theory to imply that reproduction is the reason why organisms grow old. Can this really happen?
The book uses several arguments in support of this argument:
Even if an organism does not age, it would still die from accidents. Therefore, reproduction becomes a higher priority for the organism than repairing and maintaining its body in order to survive over generations.
Consider two organisms, one that ages and one that does not. Now, if the one that ages can 'tune' its rate of aging so that its life expectancy is more or less the same as that of its non aging peer, it will suffer little loss of lifespan and gain a lot of reproductive success in return, giving it a selective advantage.
The book argues that by aging, organisms reduce the cost of dead bodies. For example, if we don't age, all the people dying would be healthy and robust, implying all the energy gone into maintaining health would be wasted. But if, strategically, we start 'spending' health to gain extra reproductive success, we end up gaining what we would otherwise waste. All the really old people in an aging world like ours become corpses even before dying, implying less loss involved.
So, here is my question:
Is reproduction one of the major causes for ageing? Is ageing a strategy to increase reproductive success, as described in the theory above? Does life history theory imply that a 'well fed' individual will strategically age itself to gain a selective advantage? Is that it? Is that why we age?
Some experiments that favour the above theory:
- It has been shown in 'hundreds of dietary restriction experiments' done on animals that a decreased rate of reproduction and of aging go hand in hand.
- An increase in the lifespan of eunuchs and castrated animals has been confirmed in many experiments.
It has been observed that if a lactating female lacks calcium, the bones in her body are demineralized to nourish her offspring, implying a higher priority towards the child than her own body, which makes sense because the child would outlive her.
Experiments have confirmed that the cost of ejaculate in male adders and Japanese macaques is non-trivial.
It should be noted that this theory assumes life history theory to be correct, and is therefore supported by all experiments that support life history theory.
After reading disposal soma theory, as suggested by rg255 in the comments, I can see that the theory discussed in this book is disposal soma theory with an extra assertion that the best life strategy of any organism is not to have 0 aging, but to have a species specific rate of aging, in order to reduce waste of resources through dead bodies and increase reproductive success.