Why do our genes kill us? Evolutionary explanation

In a post about aging and menopause as genetic mechanisms of population control, I mentioned that I consider aging as one of the varieties of the process of programmed phenoptosis (killing an individual). In the discussion, the expected salmon surfaced, with belly belly up - the poor man sharply kills hormone release almost immediately after spawning. For me, salmon is a symbol of the suicide program embedded in us, but there is nothing extraordinary in it - there are plenty of examples of active, abrupt phenoptosis in nature.

The most simple and well-known such examples are monochrome (or monocarp) plants: wheat or corn, for example. Or flowers. And among them there are perennial species, and if some of them remove the flowers in time, then these plants will not die, but continue to live, and perhaps even bloom again. At the same time, some trees live for millennia. This perfectly demonstrates that there are individuals with active phenoptosis, and there are individuals without it. Which means that biological systems do not necessarily grow old .

By the way, there is active suicide in unicellular organisms - yeast, for example. So, the old yeast goes into apoptosis, when resources begin to be missed, and the population exceeds a certain limit. And if “hungry times” come, then up to 95% of the population can go into apoptosis, turning into food for the remaining 5%, which transform into disputes and try to wait for better times in order to revive the colony.

Among animals, there are also enough examples of programmed death - in fish, insects, mammals. Here is a good, albeit incomplete review of these types:

Semelparous organisms are reproduced only once in their lives and then die. Pacific salmon

The most significant example of harsh phenoptosis among animals is the already mentioned Pacific salmon . And this is not one species, like Atlantic salmon, but the whole genus Oncorhynchus , in which there are a dozen different species, of which the majority are semelparny (that is, they are reproduced only once in a lifetime), although there are also hysterical ones like Atlantic salmon. That is, those that can breed several times, like most salmon of the genus Salmo .

It has long been proved that salmon death should not be blamed for stress or exhaustion from rising against the current, but the release of corticosteroids. Firstly, for some reason, intermittent salmon cope with stress very successfully, and they, just like semelparnye, each spawning cycle undergo the whole of this whistle dance with a rise against the current. Secondly, there are salmon species living in lakes without access to the sea, which are thus free from the need to struggle with the current before spawning (that is, there is no place for physical exhaustion), and they die after spawning anyway. Finally, even in artificial conditions, without any stress, the semelparnye salmon still die after breeding.

About insects, I generally keep quiet - there are thousands of species dying immediately after they leave offspring: from the known May beetles or butterflies, to my favorite cicadas, which can live for 17 years patiently in the larvae stage, only for to hatch and die together in a few short weeks.

There are also examples among our close relatives. Males of the marsupial mouse die after mating due to the same release of corticosteroids as salmon. A similar fate befalls mammals and a red-haired rat and a smoky mouse.

Therefore, it is naive to believe that an active suicide program cannot arise in the process of evolution. Such examples at least a dime a dozen. Accordingly, a more benign version of such a program called aging in no way contradicts evolutionary theory, if only because there are empirical facts of the presence of even sharper programs.

And, yes, the existence of programmed death in different species confirms the fact that evolutionary selection is carried out at different levels, and not only at the level of the individual. For many evolutionary biologists of the old school this is heresy, since they grew up on the dogma of “group selection can not be!”, But dogmas do not cost anything if they are refuted by the facts. Therefore, today many biologists are inclined to the so-called multi - level selection - from genes to cells to individuals to groups:

And there is a lot of evidence supporting group selection. Starting with the very existence of multicellular organisms. After all, if cells did not learn, at the expense of their personal interests, to put the interests of their colony higher, which later received the title “organism” - and the colonies in which the vast majority of cells are doomed to death (since only sex reproduces), then no multicellular cells would appear . And that altruism, which is demonstrated by yeast, social animals, and even people who are ready to die for their children, relatives, friends and their people, would never have appeared without group selection.

By the way, sexual reproduction is also poorly explainable without group selection. From the point of view of individual selection, it would be much easier and more profitable for any organism to share budding. But for a gene pool, it is better to mix with each other, creating more and more new combinations of replicators, thus increasing their chances of long-term survival and prosperity.

Exactly the same story with aging. It provides a gene pool of each population with insurance against extinction due to overpopulation. And with this point of view, some opponents of the programmed aging agree. True, then I do not really understand what they mean by programming. For me, the fact that aging gives the population an evolutionary advantage suggests that evolution had to actively sharpen the mechanisms of both aging itself and its protection against hacking. And that is why we almost never observe successful crackers of the aging program in nature - even if someone could stop aging and fix such a mutation in its progeny, its population would still die out due to a demographic catastrophe. Exceptions in the form of hydra or able to survive the glacial period of plants for thousands of years only confirm the rule.

At the same time, the strangeness of the situation among gerontologists and population geneticists is that the adherents of the programmed aging hypothesis are a minority. The heated debate about the nature of aging raged in the middle of the 20th century, but then for some reason faded away. Moreover, they died out not because this very nature of aging was unequivocally established, but because groupthink won - a phenomenon familiar to anyone who read the novel “The new dress of the king” by Andreas:

Group thinking (eng. Groupthink) - a psychological phenomenon that occurs in a group of people, within which conformism or the desire for social harmony lead to incorrect or irrational decision-making. Members of the group are trying to minimize conflict and achieve a unified solution without sufficiently critical assessment of alternative points of view, actively suppressing divergent opinions and isolating themselves from outside influence.

In such a situation, like-mindedness acquires more value than following logic and rational thinking. At the same time, the level of conformism increases significantly, information essential for the group’s activities is subject to a tendentious interpretation, and unwarranted optimism and conviction of the group’s unlimited possibilities are cultivated. Information that is not consistent with the accepted line is ignored or significantly distorted by team members. As a result, one gets the impression of unanimous decision making. Group thinking can have far-reaching social and political consequences: there are many examples in history of the tragic mistakes made as a result of such decisions.

So, the debate at the end of the 20th century came to naught because the neo-Darwinian camp, which a priori denies group selection, prevailed in academic circles, forcing all its new adherents to swear that the king's dress is quite a nothing. And while in the 2000s, outsider Mitteldorf did not come to this holiday of conformism and did not shout that the king was naked, there was no new debate about the nature of aging. But since then, the debate has resumed, and the debate is serious. Moreover, the paradigm of multilevel selection, as I mentioned, is being adopted today by more and more scientists.

The history of the academic confrontation between the two camps is well described by the famous professor of ecology and evolutionary biology, Michael Rosenzweig, in his preface to Josh Mitteldorf’s latest book, Aging - Adaptation as a Result of Group Selection . Here is what he says, read, I was not too lazy to translate:
If you say that natural selection changes Life for the benefit of species, almost any biologist specializing in evolution will protest: “No, no, no! Natural selection enhances the fitness of individuals! ”

Is there any difference? If individuals improve, does the appearance improve? Not always. Consider individuals of predators. If predatory individuals improve to the maximum, they can completely destroy all prey! What is good for the individual can destroy the whole group. And here comes a paradox.

Is it possible to avoid it? Can natural selection increase the chances that our predator will behave efficiently? Or does he doom him, like Samson, to death under the arches of the temple, the columns of which he himself is trying to destroy?

How to make evolution produce individuals that are aging, and how to make it produce prudent predators, are closely related problems. Both increase the likelihood that a group of such individuals will survive. This may sound like a great idea, but evolutionary generations have resisted all evidence that it exists, because they could not come up with a mechanism that could withstand the selfishness of natural selection. In the end, "the effect of aging on an individual is completely detrimental , as it depletes its ability to survive and reproduce."

But, dear biologists, hold on to your hats! "The facts show that aging is not selected despite its fatal consequences for the individual, but because of them." Oh! This book will blow your mind. And the more you think that you know everything about evolution, the greater will be the fragmentation field.

In science, facts ultimately rule. And over the last quarter of a century, these facts have accumulated. Mitteldorf treats them and treats them with respect. They range from computer modeling - which contrasts prudence with egoism - to the genetics and biochemistry of aging. And the totality of this evidence, loudly declares: “Aging is an adaptation. Aging is evolving. ”

But! If you come here for evidence and arguments against evolution, then you are wasting time. Mitteldorf does not argue with evolution or natural selection. In no case. On the contrary, it strengthens the evidence base in favor of one of the mechanisms of evolution - group selection. And thanks to this, evolutionists will be able to explain even more biological mysteries. And those puzzles that confront even the most intelligent supporters of individual selection will fall under the blows of the group selection. The first in a series of such riddles, by the way, is the riddle of sexual reproduction, and Mitteldorf gives her a brief analysis.

Evolutionists have long known about group selection theory, and have long since rejected it. Rejected due to the fact that individuals die faster than their groups die. Therefore, they believed, any mutation that reduces the mortality of an individual would suppress any opposite gene that reduces the risk of extinction of the entire group. Case is closed! Mind too.

And as if in order to specifically aggravate the situation, the first work accepted for publication in favor of group selection (Lewontin & Dunn, 1960) modeled a system of semi-isolated families of mice and a somewhat strange family of alleles (genes) called tailless . Most male mice homozygous for this allele have zero evolutionary survival: either they die before birth, or they are simply barren. Even though heterozygotes multiply, the tailless allele they carry is found in their offspring with a frequency of about 95% (instead of 50%). In other words, compared with wild types, tailless alleles have a competitive advantage when fertilizing eggs. Otherwise, the tailless ones would be eliminated by natural selection.

Tailless alleles are highly selfish. Levontin and Dunn have shown that if the population of the muscular semi-isolate is small, then tailless alleles can destroy the entire population in one unhappy generation. With such high rates of group extinction, group selection is where to roam in order to demonstrate their strength. Tailless and wild type remain in the gene pool, because both group selection and individual selection have their influence.

I remember, while still a graduate student, I read the above-mentioned work of Lewontin & Dunn at a training seminar. She served as a special occasion; an event that is so difficult to achieve that it just shows the improbability of group selection. All agreed: we would be in perfect order if we never spent a single minute more attention to group selection in life.

Around the same time, V.C. Winn-Edwards published his massive collection on the empirical facts of pronounced "zealousness" in wild animals. He had no mechanism and no mathematics. Therefore, his work caused only our cries and vilification. We, the disciples, have taken a tacit oath to ignore it.

In 1962, we faced the greatest challenge. Richard Levins published his foundational article on suitability in heterogeneous environments (Amer Natur 96: 361–373). We read and discussed his work, and everyone agreed: “Excellent work, yes, but his models are based on an unproven mechanism, namely group selection.” We covered this inconvenient fact under the carpet and continued to admire the rest of his work.

One day, at a meeting, I tried to directly challenge Levins' faith in group selection, but he remained unmoved. He was a Marxist before becoming a scholar. Thus, belief in group selection was an integral part of his thinking, because without group selection, Marxism would have failed. Since this was unthinkable for him, group selection should have been a reality.

I think that you are already well aware of the picture: two factions, one of the true supporters of group selection, who have never subjected him to scientific trials; and the other, all of us, who equally firmly believed that group selection should not be taken seriously.

And now, half a century later, at the age of seventy-five, I suddenly write a very laudatory preface to the book, the culmination of which is the demonstration that group selection is real. When I was twenty-five, I would rather use such a book to make a fire. What happened?

And Josh Mitteldorf happened. And Greg Pollock, too. And a lot of biochemistry, which showed us the various intricacies of the aging process. At the same time, I am ready to admit that all the brilliant biochemistry in the world would not have helped me personally. First, I am biochemically illiterate; I deliberately leave this field to others. But even if I understood biochemistry, it would not change my opinion: I would dump all the biochemical advances in one pile as submicroscopic empirical examples, and otfutolil them into the already existing bunch of examples from Winn-Edwards. I needed an evolutionary mechanism, and even Richard Levins could not show it to me.

On March 20, 2000, being the chief editor of Evolutionary Ecology Research , I received a manuscript of the article. It was from Josh Mitteldorf, and this article was the beginning of my personal intellectual revolution. It discussed the phenomenon of increased longevity caused by calorie restriction, which is an important topic that Josh fully covers in the book. Then, on November 5, 2002, I took another blow that made my beliefs shake even more, namely, the manuscript of the article “Aging is evolutionarily selected for its own sake”. Heresy, pure heresy!

Thank God, I always keep my scientific brain away from the editorial brain. Being an evolutionist, I wanted to reject this manuscript, but as an editor, I saw her courage, and felt obliged to give her a chance to see the light. And for good reason. Mitteldorf worked on the missing part of the group selection, its mechanism. It took me a year to get rid of prejudices, and as a result, the article went through an academic test and was published (Evol Ecol Res 6: 937–953, 2004). Then came a bold theory that finally cut the road back: “The chaotic dynamics of the population and the evolution of aging” (Evol Ecol Res 8: 561–574. 2006). This theory is the main thesis of this book: " Aging and regulated deadlines have evolved to stabilize ecosystems ."

Let me summarize. Do you believe in population dynamics? Fine. Then you must understand that aging is an adaptive consequence of "variation in population size that is not fully deterministic." After all, we do not know a single species with a fully deterministic population size. Proven.

Now you understand why I warned you that this book will blow your mind?

While the status quo about the impossibility of group selection was attacked on the one hand by Mitteldorf, on the other he was attacked by Gregory Pollock, whose manuscripts I received on June 11, 2003 (On suicidal punishment among Acromyrmex versicolor cofoundresses: lack of personal interests, Evol Ecol Res 6: 891–917 (2004) and 14: 951–971 (2012)). And then the status quo was put in a foolish light by theoretical simulations of Simon and Nielsen (Numerical solutions and animation of group selection dynamics (Evol Ecol Res 14: 757–768 (2012)). My intransigence was replaced by acceptance, albeit with a negative emotional aftertaste, which quite often accompanies situations where facts force a person to abandon false belief.

What is the matter? Evolutionists are not invited to abandon their view that life expectancy is under the influence of selection. The evidence for this is enormous. They are shown, however, that they must give up their belief that life expectancy is an adaptation that is subject to strictly individual selection. Instead, they must accept the likelihood that it is influenced by group selection. Undesirable and unwittingly, in order to keep our species alive, we must self-destruct following the program that leads us to death on a schedule, whether you are a mouse or a person, a mole or a mollusk — the schedule may be different, but the end is the same, and it exists by one the same reason for the good of the species.

So it's time to throw off the blinders of group thinking, and recognize that the king is naked, and aging is a program honed by group selection. And only when we know the enemy by sight, can we defeat him. Otherwise, pretending that it is not there, we will continue to look for another stopichose geroprotector, prolonging the life of mice by the same 20–30%, or starving in the hope of another 5–6 years of life.

By the way, we all know a great example of the fragility of the balance of power in multi-level selection. Periodically, the pressure of an individual (very individual, at the cellular level) selection in our cells overpowers the pressure of a higher level of the hierarchy, and they decide to shake the antiquity and, recalling their unicellular past, raise a rebellion against the tyranny of the sexual line. Yes, yes, I'm about cancer. The fact that cancer is very genetically heterogeneous and that it happens in almost all cell types, from skin or brain to blood cells, suggests that it is based on a fundamental biological process. The cell wants to share, and does not want to die.

And you can understand it. If it is still possible to cope with the desire to share, then it is very difficult to cope with the desire not to die. Because death sucks.

Source: https://habr.com/ru/post/404671/

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