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One of the most often-cited facts about human life, compared to those of other animals, is that the main reason we live so much longer is modern medicine. Because we can treat illnesses that would previously affect lifespan, we are far more likely to live greatly extended lifespans. However, this leads to two possible (conflicting) logical conclusions:

  1. People who by chance didn't get deadly diseases before modern medicine would live as long as people today, meaning the ability for any individual to survive ninety or more years, far longer than nearly all animals, is unrelated to modern medicine.
  2. Every illness one experiences weakens the body in some way, robbing it of future years. This would mean the role of modern medicine in extending lifespan is treating these illnesses to prevent the gradual reduction in lifespan.

If the first is true, then lifespan itself isn't influenced by modern medicine unless it prevents death as the direct result of a disease, and only average lifespan is affected. In other words, if nine in ten dies at age thirty due to a deadly disease, and one in ten dies at age eighty by avoiding disease, the average life expectancy is thirty five, even though an individual could by living an extremely careful life survive to reach eighty.

If the second is true, then short periods of non-deadly illnesses experienced by everyone each shorten life expectancy by a tiny amount, together decreasing everyone's lifespan to the same thirty five, rather than the effect being a result of averages.

So does each illness shorten lifespan, or is it only a result of averages that lifespan was so low pre-modern medicine, and humans always had the capacity for exceptionally-long lives?

TheEnvironmentalist
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  • in my fifth year in a medical college, i've never heard of any research on long term effects after a cured acute infection like common cold. my own suspicion is due to difficulty conducting an systematic investigation for this. – 把友情留在无盐 May 12 '15 at 00:27
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    It is an error to conclude that "human life is so long due to modern medicine". Environmental changes, especially sanitation and food availability, had rather more to do with that. – scottb Jul 10 '15 at 04:00
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    @DrRandy and jiggunjer have posted good answers. This thread is roughly a year old, with no accepted answer, and perhaps that is partly due to the third component of the question not having been answered. How would you propose anyone demonstrate scientifically whether humans have "always had the capacity for exceptionally-long lives"? You cannot, with observational/modern science do this (think scientific method, observation, repeatability). This becomes a question of history. So, you would have to consult historical (including scientifically-accurate religious) documents. – tniles May 11 '16 at 17:49

2 Answers2

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Both. Human cells largely exhibit a phenomenon called senescence - they just give up and die after they reach a certain age via a biochemical mechanism called apoptosis. The outer limit of survivability for human cells is generally understood to be in the 100-120 year range. One of the things that makes a cancer cell cancerous is the deactivation of the signals for apoptosis, making the cell effectively immortal.

At the same time, most illnesses, particularly the "lifestyle illnesses" (diabetes, hypertension, hypercholesterolemia) so common today, do induce some changes which shorten lifespan.

The most significant changes which extended human life were the development of (a) sanitation and (b) antibiotics. These together dramatically reduced death by infectious disease. Removal of early death from infection exposed these diseases of late-life and lifestyle.

JorgeArtware
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DrRandy
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    Some references in this answer would be nice. – Jez Mar 31 '15 at 19:38
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    Hm. I don't have any of my textbooks immediately to hand, as I'm not in the office, and the stuff I do have access to is paywalled and therefore not great as references. I'll see what I can come up with over the next day or two and edit in some references. – DrRandy Mar 31 '15 at 19:41
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    I thought human cells die and are created all the time. Is that not the case? E.g. skin cells during healing (and otherwise), fat cells for storage etc.etc. You wrote "The outer limit of survivability for human cells is generally understood to be in the 100-120 year range.". Does an individual cell in the human body actually ever live to be the age of its host? – Faheem Mitha Mar 31 '15 at 21:47
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    Epithelial cells die and are replaced on short cycles, but cells derived from mesothelium generally are not replaceable. This includes nerve cells, kidney cells, and a variety of other cell types. Cells from these lines are largely established by birth, or at latest, puberty. – DrRandy Mar 31 '15 at 22:37
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    I like the way you explain things @DrRandy , thank you. May I suggest that you consider taking a look at this topic of meta: http://meta.health.stackexchange.com/questions/112/what-are-reliable-sources there are some options to chose from to help you find some references to link to. For example http://www.ncbi.nlm.nih.gov/ . I consider it to be a very useful site to find viable sources of information to reference, so you don't need to spend too much time flipping through your books (I know that can be tedious). – JorgeArtware Apr 06 '15 at 22:50
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    For example "Apostosis" http://www.ncbi.nlm.nih.gov/gquery/?term=Apoptosis , you're offered a plethora of options, but let's say you chose to reference a book http://www.ncbi.nlm.nih.gov/books/?term=Apoptosis , there's a large collection of books. You can use their search engine which is useful or you could search their database using google's engine by writing the word/term followed by the keyword "site", a colon and the site you want to search, like so: "apoptosis site:ncbi.nlm.nih.gov" I found a very useful reference in like 5 seconds e.g. http://www.ncbi.nlm.nih.gov/books/NBK26873/ – JorgeArtware Apr 06 '15 at 22:55
  • I would add vaccines to the list of significant changes, unless you count them under antibiotics. – jiggunjer May 24 '15 at 19:45
  • @DrRandy, When you say "making the cell effectively immortal", doesn't that suggest that cancerous cells actually make us live longer? – Pacerier Jun 03 '15 at 20:39
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    No, because only the CANCEROUS cells are immortalized, and they steal nutrients, oxygen, and space from normal cells. – DrRandy Jun 04 '15 at 21:21
  • Senescence is a property of all terminally differentiated cells. Stem cells, however, may continue to give rise to other progenitor cells which can repopulate senesced cells. Therefore there is no direct link between apoptosis and lifespan. 2) "the outer limit of survivability .. is 100-120 years" ... this phrase has no actual meaning that I can discern.
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    @DrRandy: "but cells derived from mesothelium generally are not replaceable" ... this is incorrect. There are many examples of cells derived from embryonic mesoderm that undergo replacement: blood, bone marrow-derived cells, bone, endothelial cells, fibroblasts, etc. – scottb Jul 10 '15 at 04:06