Description
200 years ago, the human lifespan was roughly 35 to 40 years long. And it has doubled in length since then.
Question
Will the human lifespan continue to expand in length?
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1$\begingroup$ Is this question about maximum human lifespan, or about population lifespan as health and general living conditions improve? $\endgroup$ – Graham Chiu Mar 20 '18 at 1:08
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$\begingroup$ @GrahamChiu it's a question about whether it's still expanding or if it's at it's maximum length. $\endgroup$ – Eevee Mar 20 '18 at 1:29
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1$\begingroup$ And what does it refer to? $\endgroup$ – Graham Chiu Mar 20 '18 at 1:31
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$\begingroup$ @GrahamChiu the human lifespan... $\endgroup$ – Eevee Mar 22 '18 at 17:04
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$\begingroup$ So, you're asking about the maximum life span any human might attain? Like a 4 minute mile. $\endgroup$ – Graham Chiu Mar 22 '18 at 17:08
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If you mean to ask whether or not humans will be able to continue increasing their life expectancy without an upper bound, the answer is no. If you're asking if people live longer now than in the past and whether we can expect to see further increases, I'd guess that the answer is yes for most of the developed world, with the exception of the United States. The same is probably true for most of the developing world; it would definitely be true in the developing world if western corporations started paying them fairly for their labor or resources, but that's getting into an answer for a different stack exchange website.
I suppose I should qualify the "no" to unbounded life expectancy, because it could come down to definitions of alive. I don't think that it is outside the realm of possibility for science to provide techniques to artificially extend life; if we can start growing organs in labs, we might be able to just go change out our heart or kidneys much like we take our cars to have the tires changed. If you could figure out a way to take care of the circulatory / nervous system, too, who knows? As it stands, though, our cells have an upper limit on the number of times that they can reproduce because we don't have enough telomerase in somatic cells to prevent the eventual shortening of telomeres (special sequence of base pairs located at the ends of DNA molecules) to the point where they no longer protect the DNA during replication and the cell eventually dies as a consequence. Hell, if we could just figure out how to take care of that we could probably chalk on some extra time - then we can see which system would be next to fail and take us out.
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You will find here on the UN World Population Prospects plenty of data and visualization about change in life expectancy over time (among other things). The data also include predictions until year 2100.
For example, here is the life expectancy data and predictions over time for men in Morocco.
and here it is for women in Norway (note that x-axis range differs between the two graphs)
I picked two random countries but the general trend is very consistent among countries.
Is the human lifespan still expanding?
Yes, life expectancy is still increasing in pretty much all countries and is expected to keep increasing.
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1$\begingroup$ @GrahamChiu What do you mean? Are you asking about the change in the maximum lifespan through time or maybe about whether a theoretical asymptote should exist? $\endgroup$ – Remi.b Feb 13 '18 at 20:45
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$\begingroup$ @Remi.b Not sure what is motivating the comments/question here but there was a recent paper (could be 5 years old now maybe? or older, time goes fast) that made a statistical argument that maximum lifespan reached a peak some years ago and has not risen since. That is, all gains in life expectancy since then have come by delaying earlier deaths, with no effect on prolonging the longest lives, and that new supercentenarian records are only because of increasing world population and nothing more. Sorry I don't have the reference. $\endgroup$ – Bryan Krause♦ Feb 13 '18 at 21:04
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$\begingroup$ There were also papers in response rebutting the original argument. $\endgroup$ – Bryan Krause♦ Feb 13 '18 at 21:05
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$\begingroup$ It might have been this one: Dong, X., Milholland, B., & Vijg, J. (2016). Evidence for a limit to human lifespan. Nature, 538(7624), 257. I'd also add that in the US life expectancy has dropped over the last couple of years. That doesn't necessarily mean the trend is not positive, of course. $\endgroup$ – Bryan Krause♦ Feb 13 '18 at 21:07
