Degradation instead of evolution?
Woe from witAnastasia Kazantseva, STRF.ru
Medicine has destroyed evolution: now it is not the fittest who survives, but the one who turned to the doctor in a timely manner.
This leads to the fact that the number of harmful mutations in the gene pool increases with each generation. Biologist Alexey Kondrashov reassures: humanity will most likely not die out from this problem, at most it will become stupid.
Alexey Simonovich Kondrashov, evolutionary biologist, professor at the University of Michigan. His name entered textbooks thanks to the term "Kondrashov hypothesis" – it explains the existence of sexual reproduction by the need to get rid of harmful mutations (or at least compensate them with a healthy copy of the same gene received from another parent). Today, the scientist is working on problems of molecular biology, such as the evolution of proteins, and is studying spontaneous mutations in drosophila populations. This fall Kondrashov came to Moscow and throughout October he gave a lecture course "Introduction to Evolutionary Biology" for MSU students. In addition to daily lectures for biologists, Kondrashov held several popular science lectures for a wide audience. One of them, "Human evolutionary Biology and health protection", was held on Thursday, October 21, at the Polytechnic Museum.
"I demonstrate by myself, if not the importance of evolutionary biology, then at least the importance of health protection, since I have no voice at all," Kondrashov, hoarse from constant speeches, begins the lecture. In fact, of course, he demonstrates precisely the importance of evolutionary biology: only the pinnacle of evolution can, without having a voice, keep the audience in a state of complete delight for two hours.
After the necessary curtsey in any biological lecture in the direction of Luke (LUCA – last universal common ancestor, the last common ancestor) and a brief explanation of the topic ("the fact that modern man is the product of a long evolution is directly related to various aspects of medicine") Kondrashov tells the audience who we are.
We are euarchontoglyresThis is the name of a warm company of mammals, united by the results of molecular genetic research, which includes us and our closest relatives.
Relatives are rats and hares, and we are tupayas, wool-wings and primates.
Wet-nosed monkeys. Our common ancestor existed less than 80 million years ago.
(Here and further – slides from A.Kondrashov's presentation)
The history of primates is the history of strange mutations that somehow survived. Firstly, our nose was damaged, and secondly, our tail. In all normal animals, the nose is moist (mucus on the nose catches molecules of odorous substances), but among primates, a suborder of dry–nosed monkeys has appeared and achieved great success. Then monkeys separated from him, whose nose is narrow and nostrils are directed downwards. And about 20 million years ago, the common ancestor of humans, great apes and gibbons lost their tail.
Most of all useful things, of course, people have lost. The dramatic change of slides from ardipithecus to modern man demonstrates how we gradually lost the fur, the grasping function of the lower limb, the large jaw and the brow arches. We acquired a large brain (1300 cm3 versus 400 cm3 in chimpanzees), and even walking upright, which creates a lot of difficulties in the process of giving birth to cubs with a large brain. (Ardipithecus ramidus, in the picture on the left, is probably the direct ancestor of modern man. Lived about 5 million years ago, had a grasping lower limb.)
Errors of evolution"Evolution has the property that it is not omnipotent.
If anyone reads Darwin carefully, “The Origin of Species…” – this book is remarkable for some of its schizophrenicity. Because the mechanism of evolution is natural selection, adaptations and all sorts of good things, but when Darwin talks about the evidence of evolution, he is talking about just those things that cannot be explained in terms of the adaptation of species to modern conditions," says Kondrashov.
Things that cannot be explained by adaptation to modern conditions could have been useful – or just harmless– a million years ago. Evolution does not create anything ideal: every time, as a result of natural selection, something more or less acceptable remains, allowing the organism to survive and give offspring. This will not necessarily be the best of the theoretically possible options. Natural selection works with existing genes and creates new structures only on the basis of those that have already arisen. There is no reason why living beings should be perfect: it is enough that they are slightly more viable than competitors.
Kondrashov's favorite example is a flounder: "A fossil flounder that floated on its side with one eye up and one eye down is 50 million years old. Since then, she has raised her lower eye to the top, having cut everything like that, but, apparently, she will never be as bilaterally symmetrical as a stingray, which at one time sat on the bottom in the right way, will not be."
Another classic example is the inverted eye. Unlike cephalopods, in vertebrates, photosensitive cells are not located on the front surface of the retina, but on the back and are blocked from incoming light by a multitude of nerve cells and blood vessels. As a result, a person catches only 10 percent of incoming photons. The main problem of such an eye structure is the existence of a blind spot, a zone without photosensitive cells through which nerve fibers must pass to transmit a signal to the brain: the vitreous body or, much worse, the retina itself easily peels off along the border of the blind spot.
A lot of evidence of the imperfection of evolution is hidden in our genome. Hemophilia type A in half of cases is not inherited from parents, but arose as a result of a new mutation: next to the gene encoding the eighth factor of blood clotting, there is a mobile genetic element that can be embedded in the middle of the semantic DNA sequence and disrupt protein production. A similar situation with cat's eye syndrome: this disease occurs as a result of the doubling of a DNA fragment, also provoked by the movements of nearby mobile elements.
According to scientists, the genome of each person contains about a thousand harmful mutations. As a rule, these mutations do not affect the ability to live and leave offspring – otherwise they would be more intensively eliminated by natural selection. Nevertheless, they can have serious negative consequences if a child inherits broken copies of the same gene from both parents (this is the main danger of closely related crosses), and can increase the likelihood of multifactorial diseases – diabetes, cancer, and so on.
Prospects of biotechnologiesKondrashov is skeptical about decoding the genome of each person.
He fully admits that in 20 years this will become a normal situation, but he is not sure that such an approach will bring noticeable benefits. He gives an example of breast cancer, the probability of which increases many times with a mutation in the BRCA1 gene. The detection of such mutations can really save the lives of their carriers, but the problem is that 97 percent of breast cancer cases occur in people who do not have a mutation in the BRCA1 gene.
There are not very many genes that are uniquely associated with some serious disorders today, and anyone can identify them in their genome (today this is an expensive service, but available in most large cities). The rest of the known harmful genes simply increase the likelihood of developing diseases to some extent, and the fact that each person has about a thousand of them casts doubt on the rationality of their research. "Well, they will tell me: Professor, there you have 84 mutations leading to hypertension, 34 mutations leading to senile dementia, and so on, and so on. And what will I do with this information? Then the doctor will tell me: well, it is necessary, there, to eat vitamins, run in the morning, there, not to drink vodka, well, and other useful things. This is all perfectly fair, but it's true without that. You can not sequence the genome for this," the lecturer says ironically.
Of all the prospects of medicine of the XXI century, Kondrashov likes mitochondrial replacement the most. Mitochondria are intracellular organelles that use glucose and oxygen to produce an ATP molecule, a battery that provides energy for all processes occurring in the cell. Mitochondria have their own DNA (according to the generally accepted hypothesis, mitochondria are descendants of bacteria that once settled inside our unicellular ancestor), and mutations in this DNA lead to severe health disorders, such as mitochondrial encephalomyopathy. Synthesizing the mitochondrial genome has already been practically learned, transferring it to the mitochondria and inserting them into the egg is a matter of technique. Kondrashov believes that this will be done in the next ten years.
The evolution of man and his tumorsNatural selection in the human population has practically no effect.
A hundred years ago, it took place: infant mortality was huge, and a child with a successful combination of genes was more likely to survive. Now this child drinks clean water, gets vaccinated, is treated with antibiotics, undergoes bone marrow transplantation or gene therapy, and every year there will be fewer and fewer genetic disorders that medicine cannot correct. In addition, the number of children, thanks to the advent of effective contraception and effective in vitro fertilization, no longer depends on the genotype of the parents (except if we assume that the genotype determines the desire or unwillingness to have children, but this topic requires a separate lecture).
While there was natural selection, it led to a number of interesting differences between different human populations. For example, the inhabitants of Tibet have about ten adaptations to life in the rarefied high-altitude air. Northern Europeans and Bantu have a common mutation, thanks to which a grown-up person does not lose the ability to digest lactose (milk sugar). Sometimes such differences between populations lead to problems: for example, the abuse of fatty and sugary foods leads to type 2 diabetes in many people, but the probability of this in an American Indian is much higher than in a European.
Now there is no natural selection, and Kondrashov's research shows that this is bad: drosophila deprived of the influence of selection, after fifty generations, fitness catastrophically decreases – and life expectancy, and egg production, and the ability to compete with other fruit flies. However, the lecturer is optimistic: he says that humanity has a chance to die faster than in fifty generations because of climate change.
Kondrashov gives an unexpected example of natural selection: it turns out that cells of malignant tumors are exposed to it in the human body. A cancer cell is always a mutant whose cell cycle control mechanisms are disrupted. If there are several different mutants in the tumor, then the most malignant of them will win: the one that multiplies the fastest. There are experiments with transplanting cancer cells, which show that with each subsequent transplant, cancer becomes more tenacious and aggressive.
On the left – metastases in the mouse's lungs after the injection of tumor cells.
On the right – metastases in the lungs of a mouse after the introduction of descendants of the same tumor,
passed through three mice and learned to reproduce very efficiently
Do I need to be afraid?During cell division, mutations occur all the time, and it is thanks to this that evolution is generally possible.
Biologists usually treat mutations with respect. Kondrashov believes that a new change in genes does not make sense at best, at worst it does harm, and it can be useful with negligible probability. The audience is worried – is genetic variability not needed at all? The lecturer explains his position:
– Of course, there are cases when genetic diversity is good – well, if you are a Negro, then it's good to be black, if white, then it's good to be white. Moreover, there are these terrible cases of advantages of heterozygotes. Well, sickle cell anemia is a well-known case, and, apparently, there are Jewish... Ashkenazi Jews have ghetto diseases. If you have been living in a ghetto for fifteen hundred years, the main factor of mortality is tuberculosis, and if you have a lysosomal enzyme half–spoiled, then for some reason it supposedly protects you from tuberculosis a little. And such things as Tay-Sachs disease and others, which are found in huge numbers among Ashkenazi Jews, apparently, the result of such, therefore, such genetic variability. But I suggest treating tuberculosis not by carrying Tay-Sachs disease, but in some more human way.
From the lecture, the audience realized that the human gene pool is getting worse and worse, and biotechnologies are still not so perfect to fix everything. Therefore, most of the questions boiled down to the classic "what to do?" Kondrashov reassures: nothing needs to be done yet. Humanity has other problems:
– And now it [natural selection] is not completely turned off, but in some populations like Japan, its shutdown is very close to complete. But this phenomenon of literally recent decades, that is, this process of uncontrolled accumulation of harmful mutations – it has not yet been launched in all populations, it has just begun. But I really don't want to dramatize, because these are all too serious things to dramatize. And there are so many challenges facing humanity that can destroy everyone on the scale of one or two generations, that it is somehow irresponsible to think about what will happen in ten generations ... that is, not to think, but to spend some resources on it.
What exactly threatens humanity with the accumulation of harmful mutations? It turns out that first of all we will be stupid. Perhaps, thanks to this, the question of the fate of humanity will cease to worry us:
– It is clear that the consequences for a person are bad if my grandson has 20 more harmful mutations than me, and my great-great-great-great-grandson has 200. Clearly, this is bad. What will it lead to? Well, apparently, people will get stupid, first of all, because most of our genes are expressed in the brain, so this is the biggest target for these harmful mutations.
Portal "Eternal youth" http://vechnayamolodost.ru26.10.2010