The famous biologist, paleontologist and popularizer of science Alexander Markov is asking this question.
In his book Human Evolution: Monkeys, Neurons, and the Soul, he says that there can indeed be cause for concern. And this reason is the so-called weakly harmful mutations, each of which has little effect on the life and health of an individual, but when a lot of them accumulate, the effect is quite noticeable.
I must say that everyone has weakly harmful mutations. Each child carries in his genome probably about ten such mutations that his parents did not have. Therefore, it is clear that if some kind of natural selection did not exist at all (this can, of course, only be imagined, since it always exists in life), then rather quickly this species would simply become unviable.
King Charles II of Spain (Possessed) was extremely sickly due to bad heredity / Wikimedia Commons.
Suppose, for example, that we are trying to save one such endangered species and we have only a male and a female left. After they have offspring (let's say that in each generation we, for whatever reason, can get only two individuals - a male and a female), we cross them together. Discarding for simplicity the problem of inbreeding (crossing of closely related forms within the same population of organisms), we get another generation - a new male and female. We cross again, again we get one male and one female. After the nth number of generations, the number of accumulated mutations will become very high, the next offspring will be extremely weakened and unviable (recall the results of closely related marriages of the royal dynasties - NS). As a result, the population will simply die out.
“Without selection, any species must quickly degenerate and die. Simply because: 1) mutagenesis cannot be stopped; 2) most non-neutral mutations are harmful,”Markov writes.
This is also shown by experiments. One of them was conducted in 1997 by the famous evolutionary biologist Alexei Kondrashov and his colleagues on fruit flies. The researchers followed a similar pattern to the one we described above: they randomly took one female and one male from each generation and crossed them. After 30 generations, the flies of the experimenters fell into a miserable state - their fertility and life expectancy sharply decreased. Markov: “Moreover, they became lethargic and, according to A. S. Kondrashov, "they didn't even buzz."
Drosophila fly.
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“There is reason to believe that over the past 100 years people (at least residents of developed countries) have found themselves in conditions reminiscent of Kondrashov's experiment,” the author continues. "Thanks to the development of medicine, the invention of antibiotics, the solution of the food problem and the rise in living standards, mortality (and somewhat later, the birth rate) dropped sharply."
Poor health has ceased to be a real obstacle to procreation. Moreover, according to Alexei Kondrashov, natural selection today has practically no effect on a person at all, at least when it comes to developed countries. So the danger of the accumulation of harmful mutations in the human population is really obvious. But what is the scale of the disaster?
“The data are still insufficient for accurate estimates, but we still have some grounds for restrained optimism,” says Alexander Markov. And the thing is that modern data show that the influence of the genotype in modern people still remains. Even if our character, happiness in family life and political views, of course, are not one hundred percent, but clearly correlate with heredity, then what can we say about reproductive success. A person in whose genotype many weakly harmful mutations have accumulated is, on average, weaker, sicker, stupid and ugly than many of his contemporaries. As terrible as it sounds, it is true. Such a child, among other things, literally costs more to his parents, and therefore they will think hard before giving birth to a second. Let, thanks to the achievements of medicine,our weak and unhappy person will survive and leave offspring - this is still not enough for selection to fail. “Selection will cease to operate only if such a person, on average, leaves exactly the same amount - with an accuracy of fractions of a percent! - children, how many healthy, strong, intelligent, beautiful, symmetrical, which brought only joy to the parents (so they wanted to give birth to another one), says Markov. - Let it be only a fraction of a percent, but the reproductive success of such people burdened with a genetic load, even in the most advanced countries, will still be lower than that of carriers of a smaller number of weakly harmful mutations. Selection has not stopped - it has only become weaker, but it has not disappeared and will never disappear as long as we live in our biological bodies, and have not turned into robots. "“Selection will cease to operate only if such a person, on average, leaves exactly the same amount - with an accuracy of fractions of a percent! - children, how many healthy, strong, intelligent, beautiful, symmetrical, which brought only joy to the parents (so they wanted to give birth to another one), says Markov. - Let it be only a fraction of a percent, but the reproductive success of such people burdened with a genetic load, even in the most advanced countries, will still be lower than that of carriers of a smaller number of weakly harmful mutations. Selection has not stopped - it has only become weaker, but it has not disappeared and will never disappear as long as we live in our biological bodies, and have not turned into robots. "“Selection will cease to operate only if such a person, on average, leaves exactly the same amount - with an accuracy of fractions of a percent! - children, how many healthy, strong, intelligent, beautiful, symmetrical, which brought only joy to the parents (so they wanted to give birth to another one), says Markov. - Let it be only a fraction of a percent, but the reproductive success of such people burdened with a genetic load, even in the most advanced countries, will still be lower than that of carriers of a smaller number of weakly harmful mutations. Selection has not stopped - it has only become weaker, but it has not disappeared and will never disappear as long as we live in our biological bodies, and have not turned into robots. "which brought only joy to the parents (so they wanted to give birth to another one), says Markov. - Let it be only a fraction of a percent, but the reproductive success of such people burdened with a genetic load, even in the most advanced countries, will still be lower than that of carriers of a smaller number of weakly harmful mutations. Selection has not stopped - it has only become weaker, but it has not disappeared and will never disappear as long as we live in our biological bodies, and have not turned into robots. "which brought only joy to the parents (so they wanted to give birth to another one), says Markov. - Let it be only a fraction of a percent, but the reproductive success of such people burdened with a genetic load, even in the most advanced countries, will still be lower than that of carriers of a smaller number of weakly harmful mutations. Selection has not stopped - it has only become weaker, but it has not disappeared and will never disappear as long as we live in our biological bodies, and have not turned into robots. "as long as we live in our biological bodies, and have not turned into robots. "as long as we live in our biological bodies, and have not turned into robots."
So, everyone knows (and scientists even more so) that the reproductive success of both men and women in the modern world clearly depends on external attractiveness. This is an example not only of life observations, but also of many scientific studies.
Selection also works at the embryonic level: a fertilized cell overloaded with harmful mutations, as a rule, is "rejected" even in the early stages of pregnancy, as a result of which a woman may have a miscarriage. True, this, of course, is not enough to save humanity from degeneration, since the same processes were observed in Kondrashov's fruit flies - and, nevertheless, did not save the flies participating in the experiment from their sad future.
Markov himself has high hopes for in vitro fertilization (IVF) technology - a method of in vitro conception, which involves the creation of several "spare" zygotes (fertilized eggs), which grow to one of the earliest stages of development, and then the healthiest ones are selected for transplantation into the body of the expectant mother.
In fact, natural selection has indeed become weaker. However, according to Markov, today we may not need a strong one. After all, the number of humanity today is incredibly high - more than seven billion. No other species of terrestrial vertebrates of our size in the entire history of planet Earth can boast of such a number. “Meanwhile, the size of the population is most directly related to the effectiveness of selection on weakly harmful mutations: the larger the population, the less chances for a weakly harmful mutation to spread in the gene pool,” Markov notes.
In addition, the huge population size gives humanity the chances that rare beneficial mutations will appear in our gene pool, which may help better adaptation of the entire species. Markov also says that, despite the development of medicine, no one has canceled the special selectivity of individual citizens in relation to the choice of a sexual partner. “I personally really hope for princesses,” he writes. - If only they did not become promiscuous in connections. Dear princesses! Please remember that political correctness is inappropriate when choosing a life partner. You deserve more. Watch the fitness indicators closely. Don't confuse genuine big, beautiful and expensive peacock tails with cheap fakes."
Relatively speaking, very beautiful and successful ladies, as a rule, tend to choose just such gentlemen, and vice versa - ugly, poorly educated and unsuccessful women marry drunks and endure them all their lives (this principle exists in nature).
Moreover, the mortality rate does not always correlate with the effectiveness of natural selection. Thus, children who died of smallpox in the Middle Ages did not necessarily all were weak, just like those who died as a result of numerous wars and hunger - they may simply have been unlucky. Today, people for the most part are becoming richer, many have access to the achievements of modern medicine, therefore, such "leveling" can contribute to the fact that the genes, of course, of the "best" individuals, will be more responsible for natural selection.
Olga Fadeeva