The reason might not be for the health of the individual - as evolution emphasize reproductive fitness and not longevity.
Evolution make individuals of a specie healthy and fit until they reproduce and raise their young, and after that the evolutionary pressure becomes negative (are now competing against offspring success in limited resources).
One of the reasons we live so long is that the evolutionary pressure is not negative after reproduction; To begin with it takes 15+ years to raise human offspring to a stage where they might be able to fend for themselves. 20+ years to give them advantage in the environment. Grandparents relieving this burden for each generation greatly increases their reproductive success, far beyond procreation. This is of course similar to other animals, but the benefits are amplified by at least two major factors in humans. First the usefulness of inherited complex knowledge. And second, because of fetal underdevelopment due to birthing hip limitations in evolved bipedal locomotion.
Evolution is not a precise tool, just because there are pressure doesn't mean it will manifest or even have a chance to manifest.
No guarantee that a genetic behavior that kills parent individual after raising their young will not affect other things before that. Especially 'raising the young' is an indeterminate period that are hard to biologically determine.
Contrast that with species that don't have to raise their young, most of them (insects, salmon, etc) die right after reproduction.
Inherited complex knowledge and human society did not form until a few thousand years ago, that is about 150 generations where we can say we are 'relatively' civilized and maybe 10 where we are industrialized. That is an awful short time for evolution to do anything. Coupled that with the complete change of selective pressure in modern society (most individuals are no longer under selective pressure, but personal and cultural choice affect child-bearing way more), it's hard to say where human evolution will lead.
Inherited complex knowledge and human society did not form until a few thousand years ago
I think you are vastly underestimating millions of years to the contrary.
Tribal living had complex knowledge. Just how to make a bow, a spear, preserve food, build shelter, cloth themselves, hunt, harvest crops, treat many illnesses with local plants, coupled with the fact that it all had to be learned in great detail, first hand, for there was only oral history.
Even things such as "where are the animals" and "where are the apples" is complex, when drought, inclement weather, might cause local shortage, and traveling as the grandparent remembers "when I was young" for some alternate food means everything.
There are plants which taste like crap, but will keep you alive, but that sort of knowledge is lost unless you have Google (grandparents) around.
Have you looked at how corn meal is prepared in native cultures? I can't even imagine how many centuries, or thousands of years of trial and error that took, to make it edible.
If you yank this worm out, it typically rups in half. The remainder rots inside your flesh, usually killing you without modern medical care
Who retains that knowledge, for when an outbreak hits the tribe?
Who lives long enough, to notice over time (decades of adult life) what might cause the parasite.
Without paper, without Google, without written language, everything learned must be transferred to the next generation of grandparents. By having free time, by talking.
And grandparents can do many tasks which active hunters and gatherers cannot, for they have no time!
Repairing and maintaining weapons, fixing clothing, transport vessles, preparing food (which can take hours and hours), and so on.
Hm not true, a lot of other factors like medicine more relevant, would even say that modern human society has taken out almost all evolutionary pressure except for really bad conditions?!
Not at all, in fact modern society has added many new evolutionary pressures. E.g. by inventing birth control, society gave an evolutionary advantage to people who refuse to use birth control for religious reasons, or people whose biology is incompatible with birth control, e.g. a woman for whom the pill just doesn't work, is likely to have more children.
Yes but come on, that is so different that it shouldn't be even termed "evolutionary pressure" (in the usual original sense of survival of the fittest)?!
I mean, the female hyena gives birth through the clitoris. Not all evolutionary decisions are optimal for the individual. Some are just horrifying and weird.
>The extreme detour of the recurrent laryngeal nerves, about 4.6 metres (15 ft) in the case of giraffes, is cited as evidence of evolution, as opposed to intelligent design. The nerve's route would have been direct in the fish-like ancestors of modern tetrapods, traveling from the brain, past the heart, to the gills (as it does in modern fish). Over the course of evolution, as the neck extended and the heart became lower in the body, the laryngeal nerve was caught on the wrong side of the heart. Natural selection gradually lengthened the nerve by tiny increments to accommodate, resulting in the circuitous route now observed.
"There is an accumulating body of evidence that a decline in immune function with age is common to most if not all vertebrates. For instance, age-associated thymic involution seems to occur in all species that possess a thymus, indicating that this process is evolutionary ancient and conserved. ... we show that life history trade-offs play a key role and we highlight the possible advantages of the age-related decline in thymic function."
"The thymus begins to degenerate as early as the second year of life and continues through aging in human beings, leading to a decreased output of naïve T cells, the limited TCR diversity and an expansion of monoclonal memory T cells in the periphery organs. These alternations will reduce the adaptive immune response to tumors and emerging infectious diseases, such as COVID-19, also it is easier to suffer from autoimmune diseases in older people. "
> total loss of thymic reticuloepithelial tissue and the associated thymocytes should occur only at the age of 120 years in humans.
The thymus involution is the most obvious hard limit for Ageing beyond 120 years old. At age 70 your thymus has 100% shutdown and the only T cell immune system you have left are the old one still remaining in your bloodstream) (the half life is of 17 years)
The involution of the thymus (3% per year) has no consensual explanative theory behind it but the two main theories are:
1) a fact is that thymus involution appear by biologically controlled mechanisms, it appear too soon (teenage years) to be mainly due to a normal effect of an accumulation of damage (aging) although reducing oxidative stress reduce the rate of loss of thymus.
Another fact is that it is universal among mammals, and since a long time it is a conserved evolutionary mechanism.
Now I'd like you to appreciate for a minute how lucky we are and how absurdly kind life is with us. We are optimized for survival in a world with scarce resources.
We should have developed atrocious mechanisms that would make the human condition deep shit for increased survival but we have mysteriously not. E.g after taking your meal of the day we should go into low energy consumption mode, have much reduced muscular and cognitive abilities) except in the presence of dangers/stressor, until the next day.
As I said, mysteriously we are not too much behavioiraly optimized but that does not preclude that some mechanisms (especially ancient mechanisms) have been designed for hardcore resource contraints and therefore have surprising tradeoffs.
The thymus is an energy consuming organ but it's not needed for medium term survival. Because the t cell it has produced will still work for the next 20-30 years.
The age of reproduction in humans is well below 40 year old and evolutonarily speaking, a human leaving past its age of reproduction is an absurd inefficiency. It does not contribute much to the survival of the group and it consumes critical resources. It would often be logical to induce an instantaneous death to humans past a certain age (evolutonarily speaking). Many living beings, especially insects, die after reproduction, usually being eaten by the mother/childs.
Again nature has been kind with us, but basically thymus involution is like killing you after the age of reproduction, except it's a very slow process that reach completude at 70 years old and absolute immune absence at 120.
(note that this is only about T cells, the spleen (producing b cells) is another topic although it doesn't age well either).
So yeah this theory it the most potent to explain why the thymus involute.
Since this theory is a bit harsh for politics, researchers do not talk much about it. They fallback on a milder version where they simply say that the thymus in itself consume energy and reducing it allow for oleer people to consume less energy (or allocate it to other things) without addressing the obvious evolutonnary advantage of controlling lifespan.
Their milder theory is probably true in conjunction with mine. A backing evidence of them is that testosterone reduce the thymus, possibly for resources competition.
https://pubmed.ncbi.nlm.nih.gov/9427047/
I am one of the only transhumanist on earth to know that the thymic hormone thymalin restore thymus function and increase lymphocite T production by 680% and that this effect has been tested to lead to a 410% reduction of all cause mortality in humans.
https://pubmed.ncbi.nlm.nih.gov/33237528/
It's non use (e.g it was the trivial day 1 covid cure) is causing millions of deaths daily and induce misery in the quality of life of so many humans. Unfortunately science illiteracy is too strong for mankind to evolve past its infancy.
The same could be said about Skq1.
I have a lot of admiration for Khavinson, in fact they are the researchers I respect the most, however I am an independent meta-researcher without affiliation.
I wonder when will they finally attempt to do clinical trials in occident..
It's unclear to me how the war is affecting russian clinical trials in practice.
If the skq1 ones are stopped, that would be the most utilitaristic negative impact on mankind of the century.
At this point we could probably give best medical care to all the mouse if we wanted. We probably have cure for their cancer and now way to reverse age too.
Other day there was article about how injecting brain fluid from young mouse to old one helped its brain or sth.
https://www.science.org/doi/abs/10.1126/science.abd5926