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The main reason why it seems like it's not just a matter of "parts wearing out" is that different animals all age at different rates, but strikingly they all se
by dwohnitmok 5y ago
The main reason why it seems like it's not just a matter of "parts wearing out" is that different animals all age at different rates, but strikingly they all seem to age in similar ways.
For example while dogs have a much shorter lifespan than humans they seem to face all the same age-related declines humans face. This holds for animals close to or exceeding our mass as well. If different parts of the body wore out simply due to e.g. mechanical stress, you would expect e.g. dog joints to be perfectly healthy after 15 years since they are biologically very similar to human joints, when in fact dogs tend to still have arthritic and otherwise fragile joints at 15 (or earlier).
Everything declining together, just on different timetables in different animals, seems to suggest that aging is controlled by either a single mechanism or some interwoven set of mechanisms that cause everything to fail at the same time, rather than individual parts failing because "they wear out." If you could target that mechanism(s) then maybe you can make humans live as long as e.g. tortoises. But of course we haven't confirmed that such things exist, but the above is at least some motivation for why they might exist.
- honzzz 5y agoI would guess it is because there was no evolutionary pressure to have joints that can sustain 80 years if there are other parts of body that only sustain 18. Maybe I am missing something but I would expect that life expectancy of various parts of body of each specie converge because of that.
- dwohnitmok 5y agoEvolution is rarely so tidy in its convergence. Humans have vestigial organs and crazy anatomical features left over from our ancestors. In light of that it would be a rather stunning coincidence to find that when it comes to aging across species (!) that organisms seem to have all their systems age at the same rate simply by individual evolution of each of those systems or that all the systems are effectively immortal with nothing in-between. Without a coherent theory of senescence this is all conjecture, but there's compelling evidence that there's some set of hidden variables we aren't seeing that is "pulling the strings" when it comes to aging.
- honzzz 5y agoWhat compelling evidence?
- dwohnitmok 5y agoOn reflection evidence is too strong a word given that we don't have a good, specific hypothesis for what's going on. Observations of the sort I laid out above.