Tying it all together

So, do our mitochondria really kill us in the end?  According to the mitochondrial theory of aging, we should expect to find cells full of worn out mitochondria as we grow old.  Lane says that this is not what we find.  Worse, most of the diseases associated with aging have been linked to nuclear genes.
However, Lane goes on to explain that as mitochondria become damaged through mutation they are displaced by healthy ones that begin to divide.  When a cell is completely riddled with damaged mitochondria, it commits apoptosis.  This is why we don't see a build up of mutations, but instead see that organs begin to wither away.  The surviving healthy tissue is now under increased stress.  This explains why aging diseases are due to mutations in the nuclear genes and is a good clue to why trying to cure them all one by one is futile.  The diseases of aging simply add stress to tissues that are already under duress due to loss of cells that committed apoptosis because of worn out mitochondria.  If the mitochondria were healthy and the tissue were not withering away, we would not succumb to the diseases of aging.  The whole aging process could be delayed as it is in birds.  So what is different about birds?  Why do they live so long?  Lane goes on to explain that birds have far less free radical leakage in their mitochondria.  This problem sounds simple enough.  Doesn't this mean that more antioxidants should solve the problem?  Not so fast, says Lane.  Free radicals are actually an important signal that helps regulate energy production.  Therefore, if we wish to extend lifespan by reducing free radical leakage, then the chemical receptors that detect free radicals must be enhanced to be more sensitive so that these signals are not blotted out.  This is why rats have such a short lifespan.  having a more refined detection system is a big evolutionary feat and there has to be a payoff a lot bigger than just extended life.  Birds do have a special need: powered flight.  Lane also points out that while humans don't live nearly as long as birds, we are much better off than other similarly sized mammals.  So that means humans must have recently been under strong selection for longer lifespans and probably already have more sensitive
free radical detection equipment than other mammals.  Lane believes that we might find we could significantly increase lifespan by tweaking just a few genes.
So what special selection pressure have humans been under for longer lifespan?  It could have been a feedback loop of caring for their elderly and selection for longer lifespan.  Therefore, there would be selection for behavior where humans tend to care for those who cannot care for themselves.  In my last post, I linked this kind of caring with a tendency to have compassion and care for all disabled including our children.  See, I told you I'd tie it all together!