Genes and behavior: humans are just like butterflies and birds
Genes control behavior, and behavior is controlled by genes Alexander Markov, "Elements"
The journal Science has published a series of review and theoretical articles on the relationship of genes and behavior. Recent data from genetics and neuroscience indicate the complexity and ambiguity of this relationship. Genes influence even such complex aspects of human behavior as family and social relationships and political activity. However, there is also a reverse influence of behavior on the work of genes and their evolution.
Genes influence our behavior, but their power is not unlimitedIt is well known that behavior largely depends on genes, although there is no need to talk about strict determinism in most cases.
The genotype does not determine behavior as such, but rather the general principles of building neural circuits responsible for processing incoming information and making decisions, and these "computing devices" are capable of learning and are constantly being rebuilt throughout life. The lack of a clear and unambiguous correspondence between genes and behavior does not contradict the fact that certain mutations can change behavior in a very specific way. However, it must be remembered that each behavioral trait is determined not by one or two, but by a huge set of genes working in concert. For example, if it is found that a mutation in a gene leads to loss of speech, it does not mean that "scientists have discovered the speech gene." This means that they have discovered a gene that, along with many other genes, is necessary for the normal development of neural structures, thanks to which a person can learn to talk.
This range of topics is the subject of behavior genetics. Review articles published in the latest issue of the journal Science provide a number of striking examples of how changes in individual genes can radically change behavior. For example, back in 1991, it was shown that if you transplant a small fragment of the period gene from the Drosophila simulans fly to another species of flies (D. melanogaster), transgenic males of the second species begin to perform the mating song of D. simulans during courtship.
Another example is the for gene, on which the activity of searching for food in insects depends. The gene was first found in drosophila: flies with one variant of this gene search for food more actively than carriers of another variant. The same gene, as it turned out, regulates the eating behavior of bees. However, it is not the differences in the structure of the gene that play a role here, but the activity of its work (see below): in bees collecting nectar, the for gene works more actively than in those who take care of the young in the hive. How did it happen that the same gene similarly affects the behavior of such different insects with completely different levels of intellectual development? There is no clear answer to this question yet. Below we will encounter other examples of amazing evolutionary conservatism (stability, immutability) of molecular mechanisms of behavior regulation.
The Baldwin Effect: Learning Guides EvolutionThe relationship between genes and behavior is not at all limited to the unidirectional influence of the former on the latter.
Behavior can also influence genes, and this influence can be traced both in the evolutionary time scale and throughout the life of an individual organism.
The changed behavior can lead to a change in selection factors and, accordingly, to a new direction of evolutionary development. This phenomenon is known as the "Baldwin effect" (Baldwin effect) — after the American psychologist James Baldwin, who first put forward this hypothesis in 1896. For example, if a new predator has appeared, from which you can escape by climbing a tree, victims can learn to climb trees without having an innate (instinctive) predisposition to this. First, each individual will learn a new behavior during life. If this continues long enough, those individuals who learn to climb trees faster or do it more deftly due to some innate variations in body structure (slightly more tenacious paws, claws, etc.) will receive a selective advantage, that is, they will leave more descendants. Consequently, selection will begin for the ability to climb trees and for the ability to learn it quickly. Thus, a behavioral trait that initially appeared anew each time as a result of lifelong learning may eventually become instinctive (innate) — the changed behavior will be "inscribed" in the genotype. Paws at the same time, too, are likely to become more tenacious.
Another example: the spread of a mutation that allows adults to digest milk sugar lactose occurred in those human populations where dairy farming came into use. Behavior has changed (people started milking cows, mares, sheep or goats) — and as a result, the genotype has changed (the hereditary ability to digest milk in adulthood has developed).
The Baldwin effect is superficially similar to the Lamarckian mechanism of inheritance of acquired traits (the results of exercise or non-exercise of organs), but it acts quite Darwinian: through a change in the vector of natural selection. This mechanism is very important for understanding evolution. For example, it follows from it that as the ability to learn grows, evolution will look more and more "purposeful" and "meaningful". It also makes it possible to predict that a positive feedback may occur in the development of intelligence: the higher the learning ability, the higher the probability that selection for an even greater learning ability will begin.
Social behavior affects the work of genesBehavior also affects the work of genes during the life of an organism.
This topic is developed in detail in an article by Gene Robinson (Gene E. Robinson) from the University of Illinois (University of Illinois at Urbana-Champaign) with co-authors. The paper examines the relationship between genes and social behavior of animals, with special attention paid to how social behavior (or socially significant information) affects the work of the genome. This phenomenon has been investigated in detail relatively recently, but a number of interesting findings have already been made.
When a male zebra amadina (Taeniopygia guttata) — a bird from the family of weavers — hears the song of another male, the egr1 gene begins to express (work) in a certain part of the auditory region of the forebrain. This does not happen when a bird hears individual tones, white noise or any other sounds — this is a specific molecular response to socially significant information.
The songs of unfamiliar males evoke a stronger molecular genetic response than the chirping of old acquaintances. In addition, if a male sees other birds of his own species (not singing), the activation of the egr1 gene in response to the sound of someone else's song is more pronounced than when he is sitting alone. It turns out that one type of socially significant information (the presence of relatives) modulates the reaction to its other type (the sound of someone else's song). Other socially significant external signals lead to the activation of the egr1 gene in other parts of the brain.
Oddly enough, the same gene plays an important role in the social life of fish. "Elements" have already written about the complex social life and remarkable mental abilities of the aquarium fish Astatotilapia burtoni (see: Fish have the ability to deduction, "Elements", 30.01.2007). In the presence of a dominant male winner, the subordinate male fades and does not show interest in females. But it is worth removing a high-ranking male from the aquarium, as the subordinate is rapidly transformed, and not only his behavior changes, but also his coloring: he begins to look and behave like a dominant. The transformation begins with the fact that the egr1 gene, already familiar to us, turns on in the neurons of the hypothalamus. Soon these neurons begin to intensively produce the gonadotropin-releasing hormone (GnRH), which plays a key role in reproduction.
The protein encoded by the egr1 gene is a transcription factor, that is, a regulator of the activity of other genes. A characteristic feature of this gene is that a very short—term external influence (for example, one sound signal) is enough to turn it on, and the activation occurs very quickly - the time is counted by minutes. Its other peculiarity is that it can have an immediate and very strong effect on the work of many other genes.
egr1 is far from the only gene whose work in the brain is determined by social stimuli. It is already clear that the nuances of social life affect the work of hundreds of genes and can lead to the activation of complex and multilevel "gene networks".
This phenomenon is studied, in particular, on bees. The age at which the worker bee stops caring for the young and begins to fly for nectar and pollen is partly predetermined genetically, partly depends on the situation in the team (see: The gene regulating the division of labor in bees has been identified, "Elements", 13.03.2007). If the family lacks "getters", young bees determine this by reducing the concentration of pheromones released by older bees, and can move on to collecting food at a younger age. It turned out that these odor signals change the expression of many hundreds of genes in the bee brain, and especially strongly affect the genes encoding transcription factors.
Very rapid changes in the expression of multiple genes in response to social stimuli have been detected in the brains of birds and fish. For example, in female fish, when they come into contact with attractive males, some genes are activated in the brain, and when they come into contact with females, others are activated.
Relationships with relatives can also lead to long-term stable changes in gene expression in the brain, and these changes can even be transmitted from generation to generation, that is, inherited almost completely "Lamarckian". This phenomenon is based on epigenetic modifications of DNA, for example, on the methylation of promoters, which leads to a long-term change in gene expression. It was noticed that if a mother rat is very caring towards her children, often licks them and protects them in every possible way, then her daughters are likely to be the same caring mothers. It was thought that this trait was genetically predetermined and inherited in the usual way, that is, "recorded" in the nucleotide sequences of DNA. It was also possible to assume cultural inheritance — the transfer of a behavioral trait from parents to descendants through training. However, both of these versions turned out to be incorrect. In this case, an epigenetic mechanism works: frequent contacts with the mother lead to methylation of promoters of certain genes in the brain of baby rats, in particular genes encoding receptors on which the response of neurons to certain hormones depends (sex hormone estrogen and stress hormones — glucocorticoids). Such examples are still rare, but there is every reason to believe that this is just the tip of the iceberg.
The relationship between genes and social behavior can be extremely complex and bizarre. The red fire ants Solenopsis invicta have a gene that determines the number of queens in the colony. Homozygous workers with the BB genotype do not tolerate when there is more than one queen in the colony, and therefore their colonies are small. Heterozygous Bb ants willingly take care of several females at once, and they get large colonies. Workers with different genotypes have very different levels of expression of many genes in the brain. It turned out that if BB workers live in an anthill where Bb workers predominate, they follow the lead of the majority and humble their instincts, agreeing to take care of several queens. At the same time, the pattern of gene expression in their brains becomes almost the same as in Bb workers. But if we conduct the reverse experiment, that is, relocate Bb workers to an anthill where the BB genotype prevails, then the guests do not change their beliefs and do not adopt intolerance towards "superfluous" queens from the hosts.
Thus, in a wide variety of animals — from insects to mammals — there are very complex and sometimes very similar systems of interactions between genes, their expression, epigenetic modifications, the work of the nervous system, behavior and social relations. The same pattern is observed in humans.
Neurochemistry of personal relationshipsThe relationship between people until recently seemed to biologists too complicated to seriously investigate them at the cellular and molecular level.
Moreover, philosophers, theologians and humanitarians have always been happy to support such concerns. And the millennial cultural traditions that have inhabited this area with all kinds of absolutes, "higher meanings" and other ghosts from time immemorial cannot be easily discarded.
However, the successes achieved in recent decades by geneticists, biochemists and neurophysiologists have shown that the study of the molecular foundations of our social life is not hopeless at all. The first steps in this direction are described in an article by neuroscientists from Emory University, Zoe Donaldson and Larry Young (Zoe R. Donaldson, Larry J. Young).
One of the most interesting discoveries is that some molecular mechanisms of regulation of social behavior have turned out to be extremely conservative — they exist, almost unchanged, for hundreds of millions of years and work with the same efficiency both in humans and in other animals. A typical example is a system of regulation of social behavior and social relations involving the neuropeptides oxytocin and vasopressin.
These neuropeptides can work both as neurotransmitters (that is, transmit a signal from one neuron to another individually) and as neurohormones (that is, excite many neurons at once, including those located far from the neuropeptide release point).
Oxytocin and vasopressin are short peptides consisting of nine amino acids, and they differ from each other by only two amino acids. These or very similar (homologous, related) neuropeptides are found in almost all multicellular animals (from hydra to humans inclusive), and they appeared at least 700 million years ago. These tiny proteins have their own genes, and invertebrates have only one such gene, and, accordingly, a peptide, and vertebrates have two (the result of gene duplication).
In the most diverse representatives of the animal kingdom, relationships with relatives are regulated by the same substances — the neuropeptides oxytocin, vasopressin and their homologues. Fig. from the article under discussion by Donaldson & Young
In mammals, oxytocin and vasopressin are produced by hypothalamic neurons. In invertebrates without a hypothalamus, the corresponding peptides are produced in similar (or homologous) neurosecretory parts of the nervous system. When the fish isotocin gene was transplanted to rats (the so-called oxytocin homologue in fish), the transplanted gene began to work in rats not anywhere, but in the hypothalamus. This means that not only the neuropeptides themselves, but also the systems for regulating their expression (including the regulatory regions of neuropeptide genes) are very conservative, that is, they are similar in their functions and properties in animals that are very far from each other.
In all animals studied, these peptides regulate social and sexual behavior, but the specific mechanisms of their action may vary greatly in different species.
For example, in snails, the homologue of vasopressin and oxytocin (conopressin) regulates egg laying and ejaculation. In vertebrates, the original gene doubled, and the paths of the two resulting neuropeptides diverged: oxytocin affects females more, and vasopressin affects males, although this is not a strict rule (see: Males become calmer and bolder after mating, "Elements", 16.10.2007). Oxytocin regulates the sexual behavior of females, childbirth, lactation, attachment to children and a marriage partner. Vasopressin affects erection and ejaculation in different species, including rats, humans and rabbits, as well as aggression, territorial behavior and relationships with wives.
If oxytocin is injected into the brain of a virgin rat, it begins to take care of other people's baby rats, although in a normal state they are deeply indifferent to it. On the contrary, if the mother rat suppresses the production of oxytocin or blocks oxytocin receptors, she loses interest in her children.
If oxytocin causes rats to take care of children in general, including strangers, then the situation is more complicated for sheep and humans: the same neuropeptide ensures a mother's selective attachment to her own children. For example, in sheep, under the influence of oxytocin after childbirth, changes occur in the olfactory part of the brain (olfactory bulb), thanks to which the sheep remembers the individual smell of its lambs, and only to them it develops attachment.
In prairie voles, which are characterized by strict monogamy, females become attached to their chosen one for life under the influence of oxytocin. Most likely, in this case, the previously existing oxytocin system of forming attachment to children was "co-opted" to form an indissoluble marriage bond. In males of the same species, marital fidelity is regulated by vasopressin, as well as the neurotransmitter dopamine (see: Love and fidelity are controlled by dopamine, "Elements", 07.12.2005).
The formation of personal attachments (to children or to her husband), apparently, is only one of the aspects (manifestations, realizations) of the more general function of oxytocin — the regulation of relations with relatives. For example, mice with the oxytocin gene disabled stop recognizing relatives they have previously met. At the same time, their memory and all sense organs work normally.
The same neuropeptides can act in completely different ways, even on representatives of closely related species, if their social behavior is very different. For example, the administration of vasopressin to prairie vole males quickly turns them into loving husbands and caring fathers. However, vasopressin does not have such an effect on males of a close species, which is not characterized by the formation of strong married couples. The introduction of vasotocin (avian homologue of vasopressin) to males of territorial birds makes them more aggressive and makes them sing more, but if the same neuropeptide is introduced to males of zebra amadines who live in colonies and do not guard their sites, then nothing of the kind happens. Obviously, neuropeptides do not create this or that type of behavior out of nothing, but only regulate already existing (genetically determined) behavioral stereotypes and predispositions.
This, however, cannot be said about the oxytocin and vasopressin receptors, which are located on the membranes of neurons in some parts of the brain. In the above-mentioned note "Love and fidelity are controlled by dopamine", it was told that scientists tried, by acting on dopamine receptors, to teach a male non-monogamous vole to be a faithful husband, and they failed (I then noticed that "the neurochemistry of family relations continues to keep its secrets"). Three years later (that is, this year), neuroscientists still picked up the key to this mystery, and inveterate revelers were finally turned into faithful husbands. To do this, as it turned out, it is enough to increase the expression of vasopressin receptors V1a in the brain. Thus, by regulating the work of the genes of the vozopressin receptors, it is possible to create a new manner of behavior that is not normally characteristic of this type of animal.
In voles, the expression of vasopressin receptors depends on the non—coding region of the DNA microsatellite located in front of the V1a receptor gene. In a monogamous vole, this microsatellite is longer than in a non-monogamous species. Individual variability in the length of the microsatellite correlates with individual differences in behavior (with the degree of marital fidelity and care for offspring).
In humans, of course, it is much more difficult to investigate all this — who will allow genetic engineering experiments to be carried out with people. However, much can be understood without gross interference with the genome or the brain. Surprising results were obtained by comparing the individual variability of people by microsatellites located near the V1a receptor gene with psychological and behavioral differences. For example, it turned out that the length of microsatellites correlates with the time of puberty, as well as with character traits associated with social life — including altruism. Do you want to become kinder? Increase the length of the RS3 microsatellite in brain cells near the vasopressin receptor gene.
This microsatellite also affects family life. A study conducted in 2006 in Sweden showed that in men who are homozygous for one of the allelic variants of the microsatellite (this variant is called RS3 334), the occurrence of romantic relationships leads to marriage half as often as in all other men. In addition, they are twice as likely to be unhappy in family life. Nothing like this was found in women: women who are homozygous for this allele are no less happy in their personal lives than others. However, those women who got a husband with the "wrong" version of the microsatellite are usually dissatisfied with family relationships.
Several more characteristic features were found in carriers of the RS3 334 allele. Their share is increased among people with autism (the main symptom of autism, as you know, is the inability to communicate normally with other people). In addition, it turned out that when looking at other people's faces (for example, in tests where it is necessary to determine the mood of another person by facial expression), the amygdala (amygdala) is more excited in carriers of the RS3 334 allele — the part of the brain that processes socially significant information and is associated with feelings such as fear and distrust (see below).
Such studies have been conducted only recently, so many of the results need additional verification, but the overall picture is beginning to emerge. It seems that by the nature of the influence of the oxytocin and vasopressin systems on the relationship between individuals, humans are not very different from voles.
It is difficult to inject neuropeptides into the brain of living people, and intravenous administration gives a completely different effect, because these substances do not pass through the blood-brain barrier. However, unexpectedly it turned out that they can be injected pernasally, that is, drip into the nose, and the effect is about the same as in rats when injected directly into the brain. It is not yet clear why this happens, and very few similar studies have been conducted so far, but the results are nevertheless impressive.
When vasopressin is dripped into men's noses, other people's faces begin to seem less friendly to them. In women, the effect is reversed: other people's faces become more pleasant, and the subjects' facial expressions become more friendly (in men— on the contrary).
Experiments with pernasal administration of oxytocin have so far been carried out only on men (it is more dangerous to do this with women, since oxytocin strongly affects female reproductive function). It turned out that oxytocin improves men's ability to understand the mood of other people by facial expression. In addition, men begin to look into the eyes of the interlocutor more often.
In other experiments, another amazing effect of pernasal administration of oxytocin was found — an increase in credulity. Men who have been injected with oxytocin are more generous in the "trust game" (this standard psychological test is described in the note Credulity and gratitude — hereditary signs, "Elements", 07.03.2008). They give more money to their partner in the game if the partner is a living person, however, generosity does not increase from oxytocin if the partner is a computer.
Two independent studies have shown that the administration of oxytocin can also lead to harmful consequences for humans, because credulity can become excessive. A normal person in the "trust game" becomes less generous (trusting) after his trust has been deceived by a partner once. But in men who have oxytocin dripped into their nose, this does not happen: they continue to blindly trust their partner even after their partner has "betrayed" them.
If a person is told unpleasant news when he looks at someone's face, then this face will later seem less attractive to him. This does not happen in men who have oxytocin dripped into their nose.
The neurological mechanism of oxytocin's action is also beginning to clear up: it turned out that it suppresses the activity of the amygdala. Apparently, this leads to a decrease in distrust (people stop being afraid that they will be deceived).
According to researchers, society may soon face a whole series of new "bioethical" problems. Should merchants be allowed to spray oxytocin in the air around their goods? Is it possible to prescribe oxytocin drops to quarreling spouses who want to save their family? Does a person have the right to find out the allelic state of the vasopressin receptor gene in his partner before marriage?
While the court is on the case, oxytocin is sold in any pharmacy. However, only by prescription. It is administered intravenously to women in labor to strengthen uterine contractions. As we remember, it regulates both childbirth, egg laying in mollusks, and many other aspects of reproductive behavior.
It's time for political scientists to learn biologyAristotle, who is considered the founder of scientific political science, called man a "political animal."
However, until very recently, political scientists did not seriously consider the possibility of the influence of biological factors (such as genetic variability) on political processes. Political scientists have developed their own models that take into account dozens of different sociological indicators, but even the most complex of these models could explain no more than a third of the observed variability in people's behavior during elections. What explains the other two-thirds? It seems that the answer to this question can be given by geneticists and neuroscientists.
The first scientific evidence indicating that political views partly depend on genes was obtained in the 1980s, but at first these results seemed doubtful. Convincing evidence of the heritability of political beliefs, as well as other important personal characteristics affecting political and economic behavior, has been obtained in the last 3-4 years during the study of twins (one of such studies is described in the note Credulity and gratitude — hereditary signs, "Elements", 07.03.2008).
These studies have shown that political biases are largely hereditary, but they did not say anything about which genes influence these biases. Only the very first steps have been taken in this direction so far. It was possible to find a number of correlations between political views and allelic variants of genes. For example, the variability of the gene encoding the dopamine receptor DRD2 correlates with the commitment of a particular political party. However, these results are preliminary and need to be verified.
"Political thinking" seems to be one of the most important aspects of social intelligence (see: The key difference between human and monkey intelligence has been found, "Elements", 13.09.2007). In everyday life, we (like other primates) constantly have to solve problems of a "political" nature: who can be trusted and who cannot; how to behave with different people depending on their position in the social hierarchy; how to raise our own status in this hierarchy; with whom to form an alliance and against whom. Neurobiological studies have shown that when solving such tasks, the same parts of the brain are excited as when thinking about global political problems, making judgments about a particular politician, party, etc.
However, this is observed only among people who understand politics — for example, among staunch supporters of the Democratic or Republican Party in the United States. Democrats and Republicans use the same "socially-oriented" brain regions to generate political judgments. If you ask people who are not interested in politics to speak about national politics, then completely different parts of their brain are excited — those that are responsible for solving abstract problems that are not related to human relationships (for example, math problems). This does not mean that politically naive people have poor social intelligence. This only means that they do not understand national politics, and therefore the corresponding tasks in their minds fall into the category of "abstract", and socially-oriented contours are not involved. Disruption of these circuits is typical for autistic people who can cope very well with abstract tasks, but cannot communicate with people.
Large-scale political problems first arose before people quite recently on an evolutionary time scale. Apparently, to solve the world's problems, we use old, proven genetic and neural circuits that have evolved over the course of evolution to regulate our relationships with fellow tribesmen in small collectives. And if so, then it is absolutely not enough to take into account only sociological data to understand people's political behavior. It's time for political scientists to join forces with specialists in behavior genetics, neuroscientists and evolutionary psychologists.
Sources:1) Gene E. Robinson, Russell D. Fernald, David F. Clayton.
Genes and Social Behavior // Science. 2008. V. 322. P. 896–900.
2) Zoe R. Donaldson, Larry J. Young. Oxytocin, Vasopressin, and the Neurogenetics of Sociality // Science. 2008. V. 322. P. 900–904.
3) James H. Fowler, Darren Schreiber. Biology, Politics, and the Emerging Science of Human Nature // Science. 2008. V. 322. P. 912–914.
See also:1) Z. A. Zorina, I. I. Poletaeva, Zh. I. Reznikova.
Fundamentals of ethology and genetics of behavior.
2) Political beliefs depend on fearfulness, "Elements", 26.09.2008.
3) The biochemical foundations of love are laid in infancy, "Elements", 02.12.2005.
Portal "Eternal youth" www.vechnayamolodost.ru12.11.200
Genes, brains, and social behavior are linked by complex relationships. These relationships operate on three time scales: (i) at the level of physiology — affecting brain activity (solid lines), (ii) at the level of development of the organism — through gene expression in the brain and epigenetic modifications (line of dots), (iii) at the evolutionary level — through natural selection (dotted line). The direction of influence: pink arrows — from social relations to changes in brain functions and behavior, sea-green arrows — from genes to social behavior. Animals depicted (clockwise from top): zebra amadina (T. guttata), cichlid (A. burtoni), honey bee (A. mellifera), fruit fly (D. melanogaster), prairie vole (M. ochrogaster), rat (R. norvegicus), fire ant (S. invicta). The names of genes associated with a particular type of social interaction are given in italics on the photos. Image from the article under discussion by Robinson et al.