Negative selection

Is humanity getting stupid?

Civilization has radically changed the human environment and significantly weakened natural selection. How will this affect the properties of a person, in particular, his intelligence? Will it lead to sad consequences in the future? Or maybe it already has? This disturbing question is widely discussed in the special and popular literature. TrV-Science joins the discussion: we publish an article by Alexander Markov, Doctor of Biological Sciences, who has repeatedly spoken on this topic in his lectures.

Studying the evolution of intelligence is an extremely difficult research task with many pitfalls. Difficulties begin at the very beginning, when trying to determine the subject of the study. Does "intelligence exist at all"? Maybe we should talk about a lot of different, unrelated abilities with a completely different genetic and cultural basis? Someone, for example, copes well with mathematical problems, but is absolutely helpless in social interactions. Someone is well-versed in the terrain, but cannot learn a poem.

Apparently, it is still possible to talk about "intelligence in general". These examples of "one–sided" abilities are rather an exception. In large samples of subjects, the results of different cognitive tests tend to positively correlate with each other. That is, people who do well with some types of tasks, on average, do well with others. This allows us to talk about general intelligence, which is also called the g factor (from the words general intelligence or general cognitive ability) and which is believed to underlie the aforementioned positive correlation. Factor g can be quantified by the results shown by a variety of subjects in a variety of test sets. It is usually able to explain a significant part (about 40%) of the overall variability of these results. And most importantly, we can take one good test (for example, a standard IQ test), and we will have good reason to hope that its results will reflect the desired "intelligence" or "general cognitive abilities" with acceptable accuracy [1].

Like other phenotypic traits, intelligence is determined partly by genes, partly by the environment (in the broadest sense). If we are talking about people, then "environment" is primarily culture, again in the broadest sense (everything that is somehow determined by the accumulated experience and knowledge of previous generations). Without culture, we are not people, without receiving a huge amount of information from other people (including through intermediate media like books or web pages), we will not have any intelligence [2]. However, without a normally functioning brain, there will also be no intelligence, of course. And for the normal development and functioning of the brain, we need genes that have been polished by millions of years of natural selection. The brain, by the way, is the most "gene-intensive" of our organs: at least a third of the genes in our genome (and there are about 20,000 of them in total) are mainly expressed (that is, they work) in the brain.

It is logical to assume that allelic variants of many of these genes affect cognitive abilities. This is indeed the case, according to modern genetic research. It is shown that intelligence has a high heritability. This means that a significant part of the variability in intelligence (somewhere in the order of 10-20% in young children and 40-60% in adults) is explained by genetic differences between people. Why genes have a stronger effect on the intelligence of adults than children is a separate interesting topic (perhaps because young children have fewer opportunities to actively choose the cultural environment, environment and lifestyle corresponding to their innate inclinations, and with age, for example, slightly smarter people from birth begin to read smarter books or choose more smart comrades, becoming even smarter from this). What is important to us now is that modern humans have genes that strongly influence intelligence, which means that this trait can evolve. It should be noted here that all behavioral and psychological characteristics of a person, including intelligence, can evolve in two ways: genetically and culturally. At the same time, cultural evolution strongly influences the direction of the genetic one, and that, in turn, with some delay can have the opposite effect on the cultural one. We are now talking about genetic evolution, but we must not forget that in the case of a person, it is not just difficult to completely separate it from cultural evolution, but almost impossible.

At the same time, scientists have reason to believe that the genetic evolution of intelligence in modern people (at least in the most studied societies, designated by the abbreviation WEIRD: Western, educated, industrial, rich, democratic) is not directed in the direction that we would like. This orientation, of course, is set by culture. People may be gradually becoming stupid at the genetic level. This may be hard to believe, because phenotypically we are more likely to get smarter. This is indicated, in particular, by the so-called Flynn effect (which, however, in some countries is already fading and even turning back), as well as the incessant increase in the level of education.

The effect is an increase in the average IQ in several Western countries (where measurements were carried out) for decades, from about the 1930s to the 2000s. In the area of the 2000s, growth stopped, and in some places went into decline (the reverse Flynn effect). The effect most likely has nothing to do with genetics – it's too fast. It is assumed that it has a cultural origin, first of all it is the result of training for tests, both for IQ itself and for exam tests, such as the Unified State Exam. Improvement of living conditions is also attracted for explanation (good nutrition has a beneficial effect on the brain). The reasons for the reverse Flynn effect can be very different: the effect of training has been exhausted, education has sunk, the cultural background has degraded, etc. Again, its time scale is too short for genetic changes.

But the genetic basis of intelligence in our country, apparently, is slowly deteriorating. The following facts and considerations support this.

1. According to paleoanthropologists, the average brain volume of people stopped growing and even began to decrease by about 20-30 thousand. years ago. Over the past two million years, the brain volume of our ancestors has tripled. This is an unheard-of rate of brain growth by evolutionary standards. Considering that a large brain is an extremely expensive pleasure (it consumes a lot of calories, makes childbirth difficult, forces children to be born underdeveloped and helpless, which dramatically increases the burden on parents and the overall "price" of reproduction), its rapid growth indicates a strong selection in favor of brainy individuals or groups in which there were such individuals. In other words, our ancestors with a bigger brain left significantly more descendants than their competitors with a smaller brain. Why did our ancestors need a big brain, what advantages did it give? Most likely, these benefits were primarily associated with improved cognitive abilities. What kind of cognitive abilities suddenly turned out to be so in demand and why it was our ancestors – this is a separate interesting question that goes beyond the scope of this note (my thoughts on this matter are set out in the article [3]).

If, after two million years of persistent growth, the brain suddenly began to shrink, it suggests that we may have stopped getting smarter and even started to get a little stupid. The weak point of this reasoning is that the brain, in principle, can shrink without losing cognitive functions – for example, due to some kind of cunning reorganization and optimization. Modern people have a positive correlation between the volume of the brain and the mind, but it is quite weak. There are a lot of smart people with small brains, and vice versa.

2. Weakening of selection against mutations that disrupt cognitive functions. Mutations occur all the time: according to the latest (very reliable) estimates, each newborn has an average of about 70 new mutations in the genome, which were not present in dad and mom. If we assume that these mutations are distributed across the genome completely randomly, then we can expect that about 2-5 of them affect areas of the genome, the normal operation of which is important for the development and functioning of the brain. The calculation is as follows: functionally important sequences make up about 10-15% of the genome, the rest is garbage in the first approximation; about a third of functional sequences are important for the brain. As already mentioned, the brain is a very "gene–intensive" organ, which means that it is extremely sensitive to mutational damage. Mutations that spoil something occur much more often than those that improve. Simply because there are many more ways to ruin a well-established complex system than to improve it; this is sometimes called the "Anna Karenina principle", because, indeed, "all happy families are similar to each other, each unhappy family is unhappy in its own way."

Usually harmful mutations are rejected by selection: their carriers leave fewer viable descendants. But in humans, in the last 100-200 years, the selection against mutations that disrupt the work of certain body systems (immune, nervous, etc.), apparently, has sharply weakened. Thanks to the development of medicine and other cultural achievements, early mortality has greatly decreased in most societies, and in WEIRD countries it has completely approached zero. In addition, societies have become extremely careful to take care of people with disabilities, and indeed about everyone in a row. All this at least equalizes the chances of survival and reproduction for people with "good" and "bad" genotypes, including people who differ in alleles that affect cognitive functions. Well, if the selection against such alleles has weakened, then their frequency in the gene pool will inevitably grow. After all, we remember that new "bad" mutations arise constantly, and if they are not culled, they will accumulate. As a result, humanity will gradually become "genetically stupid". For the time being, cultural evolution, faster and more powerful than genetic evolution, will be able to compensate for this – for example, by improving the quality and accessibility of education. And then what? According to A. S. Kondrashov, the largest expert in this field, the problem of genetic degradation of mankind due to the accumulation of genetic cargo (and, by the way, we are talking here not only about mental and mental, but also about physical health) can begin to manifest itself after a dozen or two generations. And then it may be too late to do anything [5]. Here you can fantasize about the collapse of civilization and a return to savagery and barbarism. However, after that, positive selection for intelligence should probably work again.

There are a lot of weak points in these arguments. For example, the aforementioned 70 mutations are most likely a fairly clean sample, from which the worst mutations have already been removed. After all, prenatal mortality has not been canceled yet, and embryos with "bad" genes continue to die in large numbers. If society begins to take care of them as carefully as those already born, the mutational degradation of humanity can be greatly accelerated. But for now, we can hope that very few of the 70 new mutations present in every newborn actually harm the brain (certainly not five or even two). Some other objections can be cited (a special section in the final part of my two-volume book "Human Evolution" is devoted to them [6]). Most likely, we will not die out as a species from the accumulation of genetic cargo, but we may well lose many of the benefits we are accustomed to.

3. Selection against "intelligence genes". In addition to the passive accumulation of "bad" alleles due to the weakness of purifying selection, the intellectual status of humanity may be threatened by a more serious evolutionary force: a real selection in favor of these alleles, selection for stupidity. Genetic studies, including those based on such powerful modern methods as genome-wide association search (GWAS, genome-wide association studies), have shown that intelligence is influenced by many genes. At the same time, the influence of each gene individually is very small, but together they make a significant contribution to the observed variability in cognitive abilities. All this, of course, is also mediated by culture, and what is true for WEIRD societies is not necessarily true for "traditional" peoples from the conditional jungle. But in WEIRD countries, the heritability of intelligence is high, and many dozens of specific genes have already been found, variations in which affect the trait we are interested in. Scientists generally do not recommend calling these genes "intelligence genes". There are many reasons for this, including the extreme weakness of the effects of individual genes, and the presence of a bunch of other effects in addition to influencing intelligence, and the strong dependence of genetic effects on the cultural environment, and most importantly, the danger of being misunderstood by the general public and getting branded by people justifying (allegedly) social inequality. But we will still call them "intelligence genes" for brevity and with all reservations. So, studies have shown that in WEIRD countries (there is much less data for other countries), many "intelligence genes" are also "education genes" and even "wealth genes". Among them, as one might expect, the proportion of genes involved in the development and work of the brain is increased.

Thus, these three traits (intelligence, education and income) not only correlate with each other (which is well known for WEIRD countries), but are also determined in many ways by the same genes. In addition, many alleles that positively affect these traits are also correlated with good health and high life expectancy. The logic here is that a person who is exhausted by diseases is less likely to be able to fully develop his intelligence, get a good education and achieve financial prosperity, even if his diseases are not brain diseases.

It is logical to assume that many of the genetic variants associated with impaired intelligence, low level of education and poverty are precisely the "bad" mutations that disrupt the work of the nervous and other systems of the body and which were previously rejected by selection, and now have stopped.

The saddest thing is that they, apparently, not only got out of the negative selection, but also got under the action of the positive selection. It seems that the "good" alleles that increase the likelihood that a person will grow up smart, get a good education and be economically successful are slowly being culled from the gene pool and replaced by competing "bad" alleles.

The fact that in developed countries since about the middle of the XIX century, more intelligent, educated and successful (economically and socially) people leave on average fewer descendants than their less successful fellow citizens has been known for a long time. That is, there is a negative selection based on these phenotypic traits (the fact that numerous offspring of unsuccessful people receive less quality parental care ceased to have evolutionary significance at about the same time, and also in connection with a radical reduction in mortality, humanism and other cultural achievements). Major scientists, among whom was one of the creators of the synthetic theory of evolution (and at the same time mathematical statistics) Ronald Fischer, the corresponding concerns have been expressed for a long time. But only recently, genetic studies based on the analysis of the genomes of tens and hundreds of thousands of people with a known phenotype and life history have convincingly shown that selection works directly against the genes of intelligence, education and wealth. As it turned out, in order to have a reduced chance of successful reproduction (i.e., the expected number of children is below average), you do not even need to be smart, educated or rich, but only have a genetic predisposition to this. For example, a large-scale study conducted in Iceland showed that people with a large number of alleles that increase the likelihood of getting a good education leave fewer children on average, even if they do not receive a good education [7].

How can this work? For example, people with good cognitive abilities are more likely to think about the future and plan a career. Therefore, on the one hand, they are more likely to enroll in a decent college, and on the other hand, they will postpone the birth of children "for later" in order to first find a good job, buy a house, etc. And I must say that at the moment when the idea arises in a human head that it is not necessary to have children at the age of 18, but it is better to achieve something in life first, at this very moment the Darwinian fitness (reproductive success) of this person collapses with a loud crash. Especially if everything happens in the era of universal availability of family planning tools (this, by the way, is an example of how cultural evolution affects genetic). The fertile period of our life is short, and the expected number of children is associated with the age of birth of the first child with a very rigid inverse relationship.

Icelandic scientists have also shown that the frequency of occurrence of "education genes" in the Icelandic gene pool is really decreasing, and that if everything goes on like this, the average IQ of the population will fall by about three points per century (of course, without taking into account such cultural phenomena as the Flynn effect, the Flynn reverse effect, etc.). the results were obtained on samples of US residents [8] and Of the United Kingdom [9].

It is also important that the development of civilization, humanism, support for the disadvantaged and the struggle for equality of opportunities can make natural selection (if it exists in principle) more effective. After all, this is, in fact, the alignment of "environmental conditions" for all segments of the population. As a result, the proportion of "environmental" variability of phenotypic traits should decrease and the proportion of genetic variability should increase. The term "heritability" mentioned above, in the first approximation, can be defined as the ratio of genetic variability to the overall variability of a trait. If we create equally favorable development conditions for all people (which many societies strive for), then environmental variability in phenotypic traits, including intelligence, will decrease, and genetic variability will come to the fore. The heritability of traits, accordingly, will increase, and therefore selection – with its intensity unchanged – will give more tangible results (according to the well–known "breeder's equation" (Breeder's equation) R = Sh2, where R is the effectiveness of selection, S is its intensity, and h2 is heritability). In general, if negative selection based on intelligence genes is real, then humanism and concern for universal equality can enhance its effect.

How serious is all this and is it time to panic already? There is no exact answer, but, most likely, we still have some generations left before the film "Idiocracy" comes to life. 

Idiocracy (2006) is a satirical film by Mike Judge, creator of the animated series about Beavis and Butthead. The preamble shows the fate of two families with an IQ of 140 and 80. The first one postpones the birth of a child many times and ends up with the husband dying while masturbating for IVF, the second one is born into a mighty family tree. The hero of the film is a librarian with average abilities, who, due to an unsuccessful experiment, falls into the distant future (2500), where he turns out to be the smartest person in the world.

To prevent this from happening, it is necessary (at least) to seriously study everything that has been discussed here, and not to hide your head in the sand, and even more so not to stigmatize scientists who dare to take on such explosive topics.

Finally, I will note that "global stupidity" and even the collapse of civilization, in principle, can occur at the expense of cultural evolution alone, without the help of genetic evolution. Cultural evolution has been affecting our lives much faster and more radically than genetic evolution for a long time (maybe since about the time when our ancestors stopped growing brains). But that's another story.

Literature:

1. Plomin R. , Deary I. J. Genetics and intelligence differences: five special findings, 2015.
2. Henrich J. The Secret of Our Success. How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter, 2018.
3. Markov A. V. , Markov M. A. Runaway brain-culture coevolution as a reason for larger brains: Exploring the “cultural drive” hypothesis by computer modeling, 2020.
4. Jónsson H. et al. Parental influence on human germline de novo mutations in 1,548 trios from Iceland, 2017.
5. Kondrashov A. S. Crumbling Genome. The Impact of Deleterious Mutations on Humans | Kondrashov Alexey S., 2017.
6. Markov A.V. Human Evolution (in two volumes), 2011.
7. Kong A. et al. Selection against variants in the genome associated with educational attainment, 2017.
8. Beauchamp J. P. Genetic evidence for natural selection in humans in the contemporary United States, 2016.
9. Hill W. D. et al. Genome-wide analysis identifies molecular systems and 149 genetic loci associated with income, 2019.

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