Steve et al,
Sorry to say this but there’s so much we don’t know – and worse, so much we think we know but do not. The work of Amy Wagers on heart rejuvenation using heterochronic parabiosis showed that the dormant and apparently non-functional cardiac stem cells could be made to function so as to strengthen the heart – when for many years no one thought these cells important. One question that often arises with discussions of life extension (in my Biology of Aging class) is whether rejuvenated women might be able to produce babies. The standard medical answer would be “no”, simply because it is believed that women are born with their full quota of ova already stuck in the first meiotic metaphase at birth. However this is not strictly fact. Lord Solly Zuckerman ‘ruled’ that the model of all ova already being formed by birth and waiting in stasis for the hormone surge that would send them through meiosis and produce the ovum that would eventually go down the fallopean tube is a reasonable hypothesis based on the evidence (in the early 1950’s), not a matter of fact. The facts is (are) that subsequent studies in mice at least suggest that new ova are created throughout the fertile life of female mice. Which picture is the true one? In retrospect I can’t imagine that a cell can be stuck in metaphase I for decades, all its genes hidden from intracellular machinery by the compaction of the chromosome – even with nurse cells (if they do so) to feed the quiescent metaphase I ova – I still can’t imagine how a cell could maintain itself in that state for decades. I can’t remember the source (time for rejuvenation!), but some editorial somewhere said something like, “If we can’t accept this model (wrong though it be) then we have no explanation at all!” The implication being that it’s better to have a bad model than no model at all – which I think is exactly the opposite of the truth. Having a wrong model heavily ‘believed in” is much worse than having no model – because it leads you in the wrong direction – while not having a model may keep you in the same place until you do have one, and one that works. I think this is the case with aging, our ‘wear and tear’ models have led us in the wrong direction – trying to patch the lesions occurring during aging instead of aiming at the source of those lesions – which turn out to be self-imposed. Like fighting ISIS by sending in ambulances to repair the wounds inflicted by their soldiers on ours.