Is humanity degenerating?

This question is asked by the famous biologist, paleontologist and popularizer of science Alexander Markov

Olga Fadeeva, Naked Science

In his book "Human Evolution: Monkeys, Neurons and the Soul," he says that there may indeed be cause for concern. And this reason is the so–called mildly 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 mildly harmful mutations. Each child carries probably about ten such mutations in his genome, which 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 quite quickly this species would simply become unviable.

Imagine, 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 assume that in each generation, for some reason, we can only get two individuals - a male and a female), we will cross them with each other. Discarding for simplicity the problems of inbreeding (crossing 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 royal dynasties – NS). As a result, the population will simply die out.

King Charles II of Spain, possessed because of bad heredity, was extremely morbid. Juan Carreño de Miranda, 1685.

Imagine, 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 assume that in each generation, for some reason, we can only get two individuals - a male and a female), we will cross them with each other. Discarding for simplicity the problems of inbreeding (crossing 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 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.

Experiments also show this. One of them was conducted in 1997 by the famous evolutionary biologist Alexey Kondrashov and his colleagues on fruit flies. The researchers acted like the scheme we described above: randomly took one female and one male from each generation and crossed. After 30 generations, the experimenters' flies came to a pitiful state – their fertility and life expectancy sharply decreased. Markov: "In addition, they became sluggish and, according to A.S. Kondrashov, "they didn't even buzz"."

"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 the Kondrashov experiment," the author continues. "Thanks to the development of medicine, the invention of antibiotics, the solution of the food problem and the increase in living standards, mortality has sharply decreased (and somewhat later, the birth rate)."

Poor health has ceased to be a real obstacle to procreation. Moreover, according to Alexey Kondrashov, natural selection has practically no effect on humans today, at least if we are talking about developed countries. So the danger of accumulation of harmful mutations in the human population is really obvious. But what is the scale of the disaster?

"There are not enough data for accurate estimates yet, 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 whose genotype has accumulated a lot of mildly harmful mutations is, on average, weaker, sickly, stupid and ugly than many of his contemporaries. As terrible as it sounds, it's 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 one. Let, thanks to the achievements of medicine, our weak and unhappy person survive and leave offspring – it's still not enough for selection not to work. "The selection will cease to work only if such a person leaves exactly the same amount on average – with an accuracy of a fraction of a percent! – there are as many children as there are healthy, strong, smart, handsome, symmetrical, who brought only joy to parents (so they wanted to give birth to another one), – states Markov. – Even if only by a fraction of a percent, but the reproductive success of such people burdened with a genetic burden, even in the most advanced countries, will still be lower than that of carriers of a smaller number of mildly 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."

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. An example of this is not only life observations, but also a lot of scientific research.

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. However, 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 the technology of in vitro fertilization (IVF) – a method of conception in vitro, involving 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 from them 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 species of terrestrial vertebrates of our size can boast of such a number in the entire history of the planet Earth. "Meanwhile, the population size has the most direct relation to the effectiveness of selection on mildly harmful mutations: the larger the population, the less likely a mildly harmful mutation is to spread in the gene pool," Markov notes.

In addition, the huge size of the population gives humanity chances that rare beneficial mutations will arise in our gene pool, which may help the best adaptation of the entire species. Markov also says that, despite the development of medicine, no one has canceled the special selectivity of individual citizens regarding the choice of a sexual partner. "I personally really hope for the princesses," he writes. – As long as they don't become promiscuous. Dear princesses! Please remember that when choosing a life partner, political correctness is inappropriate. You deserve more. Pay close attention to fitness indicators. Do not confuse genuine large, beautiful and expensive peacock tails with cheap fakes."

Relatively speaking, very beautiful and successful ladies, as a rule, tend to choose such gentlemen for themselves, and vice versa – ugly, poorly educated and unsuccessful marry drunks and tolerate them all their lives (this principle also exists in nature).

Moreover, the mortality rate does not always correlate with the effectiveness of natural selection. So, children who died of smallpox in the Middle Ages were not necessarily all weak, as well as those who died as a result of numerous wars and famines – they may simply have been unlucky. Today, people are becoming richer for the most part, the achievements of modern medicine are available to many, therefore, such "equalization" can contribute to the fact that the genes of, of course, the "best" individuals will be more responsible for natural selection.

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