Human immortality?
I got inspired to write this article by reading a very interesting text of @thecryptofiend about the Genus Hydra (for example Hydra viridis) and its immortality.
Why must we die?
Of course reading his article may inspire thoughts about the question if (or why not) also humans could reach immortality one day in future?
To give a small part of the answer I want to focus on one of the reasons why at present we cannot live forever:
In the nucleuses of our cells are the chromosomes (in our case 23 from our mother and 23 homologous ones from the father). The DNA of these chromosomes comprises the genes which contain the necessary information to build the polypeptides of which consist our cells (and therefore also our bodies). The ends of each chromosome consist of DNA with repetitive nucleotide sequences and associated proteins called telomeres. In case of vertebrates these sequences contain the nucleotides T-T-A-G-G-G and repeat several thousand times.[1] Their function is to stabilize and protect the chromosomes. While an organism is getting older with each cell division the telomeres of its chromosomes become shorter and shorter until the cells are no longer able to divide. Then three scenarios may happen:
- Apoptosis: cells kill themselves whereupon proteolytic enzymes (caspases) play an important role.[2]
- Senescence: cells stop to grow and to divide.
- If cells divide again even if they contain already shortened telomeres (like some cancer cells do) one can observe an increasing instability of the chromosomes.
At the least when the lengths of the telomeres of too many cells of a human organism fall under the critical number of less than 4 kilobases (at birth their average length is about 11 kilobases[3]) the right moment to die has come ...
End of story? Not yet completely:
Is there any hope for immortality?
There is an enzyme named telomerase which could give us some hope. It is able to repair the telomeres at the end of the chromosomes. The problem is that firstly it is not active in all human cells and secondly its activity decreases while we are growing older. Actually studies evidence that the telomerase activity in our cells also depends on our way of life.[4] Especially stress plays an important role and chromosomes of children who suffer under a low social status exhibit shorter telomeres than average.[5]
But even living very healthy and being extremely rich won't make us immortal though. And I still didn't talk about the main problem: Adding telomerase to the cells slows down the shortening process of the telomeres but at the same time drastically increases the probability of cancer.
So what to do? To solve both problems Scientists interbred two kinds of genetically changed mice:
- Mice who produced telomerase reverse transcriptase (TERT), one of the components of telomerase.
- Mice "races" with the tumor suppressing genes p53, p16, and p19ARF.[6], [7]
The resulting transgenic offsprings reached, depending on the different combinations of tumor suppressing genes, an up to 40 % extended lifespan.
Conclusion 1 (concerning the initial question):
It could be possible that in future tumor suppressing factors combined with an increased production or donation of telomerase may also extend the lifespan of humans as well. (Actually we are very far away from reaching 'immortality' at the moment, but I needed a term to attract as much readers as possible ... :-)
Further thoughts: Is nature (is evolution) just too stupid to create everlasting life?
No! There are examples of organisms who don't switch off telomerase when aging so that in theory they could live forever (if they don't get killed by enemies or die because of sicknesses).[8]
Amazingly the concept to die and give ones genes to the next generation most of the time seems to be superior in evolution compared to the concept of immortality. The reason for that is that it allows to adapt more easily to a changing environment according to the motto "we age because the world changes" - also computer simulations seem to confirm that.[9], [10]
Conclusion 2:
From the point of view of a single individual it may be desirable to live forever but from an evolutionary perspective it is actually a big advantage that we die.
Sources:
- https://en.wikipedia.org/wiki/Telomere
- https://www.ncbi.nlm.nih.gov/pubmed/14499155
- http://www.telomer.com.tr/wp-content/uploads/2015/12/TL_in_the_new_born_AvivA_IPRF_2001.pdf
- http://www.thelancet.com/journals/lanonc/article/PIIS1470-2045%2813%2970366-8/fulltext
- http://www.deutschlandfunk.de/meldung-forschung-aktuell.678.de.html?drn:news_id=344290
- http://www.sciencedirect.com/science/article/pii/S0092867408011914
- https://www.heise.de/tp/features/Telomerase-verlaengert-das-Leben-3420854.html
- http://www.pnas.org/content/109/11/4209
- http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024328
- http://www.spiegel.de/wissenschaft/mensch/neue-computersimulation-altern-macht-die-menschheit-staerker-a-795152.html
Image from pixabay: https://pixabay.com/en/cells-human-medical-biology-health-1872666/
jaki01, Thanks so much for directing me to this post. You provide a great description of the science for longer lives. I'm really interesting in the political, ethical and social implications of this and how this could play out with existing inequalities and power dynamics. Its not hard to see some strong dystopian possibilities. It might be a tech we'd want to unlock only when we have greater capacity to colonize space and reduce the demand on the earth's already limited carrying capacity.
I am also not sure Earth could support so many immortal humans. So for this reason, it is also good that we die at some point (although with immortal beings, we could explore space to its deepest level ^^ )
Very nice post! (you may also want to check this one by @justtryme90, in the case where you would have missed it!
Yes, also very interesting, thanks to call my attention to it!
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Thanks a lot for this very detailed post on telomeres, evolution and immortality. Whether we should be immortal or not is a good question, and as for anything, we have pros and cons. Thanks for bringing the debate on Steemit!
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Nice surprise - thanks a lot! :)
There is no easy answer!
You are right for sure. But it seems to be an evolutionary advantage to die and have offspring instead to live forever, because it makes adaptation to a changing environment more easy.
Yes that is true but technology changes things!
Even if possible the question would be if it made sense to live forever and in addition give birth to new humans. There is already a huge overpopulation on earth. Where would that lead?
And I only wrote about the biological/genetic aspects of the topic. The ethical are complicated too: for example there is the scenario that technological progress would make immortality possible but only very rich people could afford the necessary "treatment" ...
Overpopualtion is overstated problem in my opinion. Longer functional lifespans will allow humanity to spread out across the universe. There are always going to be big ethical issues.
In my opinion overpopulation is not overstated - but I appreciate the fact that different people who have the same information come to different conclusions. That's what makes discussions interesting. :)
I come to my conclusion when I think about how fast we exploit the limited resources available (the amount of clean water, the number of edible fishes in the oceans, the rain forests - nearly all important resources are decreasing). Yes, we may find new ways ... start to eat insects, farmed algae or artificial food from cell cultures for example, but finally the resources are limited and we are getting more and more.
Your idea to conquer the universe is really fascinating, but considering the enormous distances I have some doubts if it will come true (and if it will be done successfully). We (or better to say our descendants) will see.
By the way, if I was god (not that I am sure that there does exist one) or whoever who constructed the universe for whatever purpose I also would have made we distances as huge as they are to make sure that such an aggressive species like Homo sapiens stays restricted to a very limited area. :-)
Yes, seems to be a very sensible idea to create a high-security wing for Homo sapiens. :)
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Nice job talking about telomere lengthening and telomerase. Research indicates as you said that we might be able to use this idea at some point to extend further our lifespans, or reverse the outward appearance of aging. However DNA replication during cellular division is not an error free process. Immortality would necessitate us coming up with a way to not accumulate any mutations, but also as you stated doing that would limit our ability to adapt to new conditions (biologically).
It's a complicated and multifaceted problem to tackle, and a quite interesting thought experiment!
Yes, thanks for pointing out the importance of mutations (but this time I just wanted to focus on one of the reasons which cause our aging, so that the article wouldn't become too long. :)
Mutations are indeed of unbelievable prominence, not only because they damage one single organism while it is aging but also because without them we would not exist at all (the concept of evolution wouldn't work anymore).
Very interesting article! I have to agree with some other people here in the comment section that it's maybe a good thing we are not immortal. That would put too much of a strain on our ecosystem. In addition, that would also prevent very evil, stupid or brutal people from leaving this planet. ;-)
Did you read the last part of the article, too? There I also state that anyway from an evolutionary perspective it was most of the time more successful to "create" mortal species ... I find the part about the computer simulations interesting as well ...
Yes, I did. What I find to be very fascinating is the fact that even though immortality is such a distant dream, there are already people pushing research in that direction. Like the "Immortality institute" (http://www.imminst.org/about) for example.
I suppose to die is one of the things many people fear most. So it is very "human" to think about how to avoid or at least to delay ones death. Most individuals understand that an even bigger number of humans caused by immortality would be dangerous for the survival of the species but that doesn't change the fact that nevertheless many people dream about being immortal ...
interesting discussion in the comments here but to ordinary person like me, if I have to live longer, I have to worry longer about jobs, expense, healthcare, taxes, what else?
You are right, life is sometimes a really hard fight ... But I guess that doesn't change the fact that you would like to live longer if possible? :-)