Throughout the history of evolution, scientists have identified two types of twins in nature: monozygotic (identical) and dizygotic twins (fraternal).
Monozygotic twins are a consequence of multiple pregnancy, which arose due to the fertilization of one egg and the development of two or more fetuses in it. The prevalence of monozygotic twins is quite low, but dizygotic (fraternal) twins are more common.
Scientists associate the occurrence of monozygotic twins with the fertilization of an egg that had two or more nuclei. Each nucleus is connected to the nuclear substance of the spermatozoon, due to which the rudiments of embryos begin to form. During the development of the ovum, at the very beginning, the laying of the chorion, amnion, and then the formation of the embryo itself. Therefore, the features of placentation in the process of the formation of monozygotic twins depend on the stage of development of the fetal egg, at which its division occurs.
Features of the phenomenon
Since ancient times, when the subtleties of genetics and anatomy were still alien to people, the birth of two completely identical people was equated to something supernatural. They could be attributed both divine and diabolical properties.
For example, the American Indians had a belief that one of these twins is a product of evil, and the other is good. Therefore, the "evil" twin was always soon expected to be expelled from the tribe.
Our Slavic ancestors believed that twins have a single soul. Therefore, one twin was never allowed to attend the wedding or funeral ceremony of the other. Also in Slavic and Indian culture, people believed that the birth of twins was a kind of natural whim. And so the people believed that such children could "negotiate" with nature itself.
But if you look at this phenomenon today, from the point of view of science, then in fact, monozygotic twins have the same genotype, as a result of which they have an amazing similarity to each other and they are always the same sex. It is for these reasons that they are called identical. It should be noted that the similarities of such children are not only portrait. Of course, these are two completely different personalities, but quite often the characteristics of behavior, habits, character, and even the choice of a profession in the future may coincide.
Scientists have always had a special interest in monozygotic twins, which is why they love to conduct a wide variety of studies involving such twins.
Not so long ago, scientists found that there are still some differences in the genomes of identical twins. And in 2008, a group of American and Swedish scientists in the course of research found that monozygotic twins can also have genetic mismatches. After studying the genomes of nineteen pairs of such twins, scientists found some mismatches in copies of DNA segments of somatic cells. Despite the fact that identical twins are almost identical, some differences have been found in the majority.
Another feature is that many brothers and sisters who were born on the same day grow up in the same environment. Twins most often receive the same gifts, toys, and in most cases they start going to the same school, and so on. Of course, they might have different interests. For example, common preferences in literature, but mothers and fathers usually read the same books to them. And, of course, no one will deliberately separate children and try to raise them in different conditions, since this is inhuman. The exceptions are those cases when fate itself separates people against their will.
A huge study was conducted in the early 80s of the twentieth century by an American psychologist, whose name is known as Thomas Buchard. In total, the objects of his research were thirty pairs of twins, who, by the will of circumstances, were separated from early childhood. One of these couples was monozygotic twins, brothers Oscar and Jack. Some time later, after the birth of the boys, the marriage broke up and as a result, the mother took Oscar to her native land in Germany. A few years later, Oskar joined the Hitler Youth, after which he became a believing Catholic. And Jack grew up with his father in Palestine, and later in the Caribbean, where he was brought up according to all the traditions of Judaism.
As a result, the meeting of the brothers took place only by the age of forty. The most surprising thing in this story is that, despite the differences in upbringing, living environment and language, there were many similarities in their behavior and characters. Both had the same temperament, preferences in both clothing style and food were very similar. But the most surprising thing was that they wore almost identical glasses and even identically cropped mustaches. Both brothers were rather scattered, and the style of their communication in families was the same.
Another example is the sisters - Lois and Louis. The girls were born in 1920 and after the birth they were separated for some time. They were brought up in different families and their levels of education, places of residence were completely different. Louise grew up in a small town and studied at the most ordinary school. And Lois lived in a big city and studied at a more prestigious institution. Although the economic condition of both families was approximately at the same level. Probably, this is precisely what served the fact that at the age of eighteen the girls entered the same institute. And as studies have shown, in terms of physical and psychological traits, the girls turned out to be extremely and incredibly similar. There was much more similarity between them than many sisters and brothers who had grown up together all their lives.
Well, another funny example was in the USA, when two monozygotic twins separated in childhood chose the same field of activity, which was distinguished by its specificity. Ultimately, both brothers soon became safecrackers.
Despite this, scientists are extremely cautious about the hereditary role. As many studies have shown, monozygotic twins have a fairly similar "criminal history" in 50-70% of cases. In dizygotic twins, this phenomenon is much less common, only about 20% of cases.
Of course, there are many stories about some kind of telepathic connection between identical twins, which you can not believe. But the fact that these children can understand each other much better than ordinary brothers and sisters has long been confirmed. Very often, as monozygotic twins grow up, it is quite difficult to form some kind of separate independent personality in themselves. After all, from childhood they are even dressed in the same clothes, read the same books, give the same gifts. Often this leads to the fact that the twins are almost inseparable throughout their lives.
Also, according to some signs, monozygotic twins should have extremely similar consciousness. For example, they may have the same passion for dishes of the same cuisine, or parting with their lovers may occur. Perhaps this is what explains the fact that in the fates of such brothers and sisters there are such strange coincidences even in small things.
Identical twins in IVF
During the IVF procedure, conception, as such, occurs in a test tube, and after about three days, the resulting embryos are introduced into the woman's uterus, where they begin their further development. And in order to increase the chance of pregnancy, doctors always place more than two embryos (from two to three) in the uterus, in the hope that at least one will take root.
In some cases, several embryos can take root at once, and in the process of implantation into the uterus, one of the zygotes divides into two more, and then identical twins begin to develop from the cell. As soon as the onset of pregnancy by IVF is confirmed, the woman is informed about the number of fetuses that have taken root, and if there are more than two of them, then in order to increase the chances of successful gestation without complications, the extra embryos are removed.
How the development of monozygotic twins will occur largely depends on the presence of one placenta and bladder.
If two fetuses are located in separate bubbles and at the same time with one placenta, then there may be a risk of "dehydration" of one of them. In other words, a "stronger" identical twin receives much more of the necessary substances. In this scenario, when the moment of birth comes, a "weak" child can be born 400-600 g less than his identical twin. In severe cases, such a baby may be slightly behind in development from his brother or sister.
It sometimes happens that on the fifth week of an ultrasound, doctors can see two embryos that they implanted in the uterus, and on the next ultrasound of the seventh or eighth week, three embryos can be clearly seen in the uterus. This can be observed in cases where one of the zygotes has separated, and as a result, monozygotic twins began to form.
As for the gender of such twins, then, as mentioned earlier, they will definitely have one, since the birth of children occurs as a result of the division of one fertilized egg and the sex will be determined after the process of fusion of the cells of the mother and father.
In the wild, many animals often have many babies at the same time, but in humans, there is one birth of twins for every 250 births of one child. Scientists distinguish between monozygotic and twins, and in colloquial speech they are also called fraternal or twins and twins.
identical twins
Identical develop from one fertilized egg, which is divided into two or more parts, which began to develop separately. Thus, all embryos receive the same set of genes and develop in approximately the same way. Such children always have the same sex and are very similar to each other, sometimes even parents cannot distinguish between them. Although sometimes they have mirror features: for example, one has a mole on the right side, the other on the left, one is right-handed and the other is left-handed. They have similar character traits, almost the same temperaments, predispositions to disease, and often even fates.
There are cases when identical twins separated in childhood, who did not know about each other, lived almost identical lives.
The cases of the birth of monozygotic twins are several times rarer than those of fraternal twins, since the division of the egg into several parts is uncharacteristic for a normal pregnancy.
fraternal twins
Fraternal twins have a different set of genes, since different sperm and eggs took part in their conception. In some cases, in women in one menstrual cycle, two or more eggs ripen at once, if all of them are fertilized, then a multiple pregnancy will begin, and two or more children will be born. These are quite common cases, in some nationalities they are very common - it is believed that multiple pregnancy is of a genetic nature.
The genotypes of fraternal twins, which are also called twins, are different, so children can be of different sexes and generally differ from each other, like ordinary brothers and sisters. It is known that with age, the probability of multiple pregnancy in women increases.
In countries where it is customary to give birth after the age of thirty, for example, in the USA or European countries, there are more cases of birth of fraternal twins.
There is another type of twins, which is called transitional between the two described - polar or semi-identical. This happens when two different spermatozoa fertilize the egg and the polar body that formed with it (usually it dies off). As a result, the embryos get a half different set of genes, the same from the mother.
Twin children who have the same heredity, as a result of separate upbringing, sometimes become more similar to each other than if they are brought up together. This somewhat unexpected fact is explained by the fact that children of the same age, who are constantly next to each other, almost never manage to do the same thing, and between such children there are rarely completely equal relations.
Despite the great similarity in a number of psychological and behavioral characteristics that is found among homozygous twins, the assertion that their psychological commonality is due only genetically is hardly justified. The conducted studies and the results obtained in them allow us to consider the influence of the environment on the mental and behavioral development of an individual as stronger than the influence of his heredity.
A comparative study of the role of heredity and environment and their influence on human psychology and behavior is usually carried out in one of the following ways:
1. Systematic variation of the conditions of education and upbringing, a comprehensive study of children who grew up in different social cultures, regions and families.
2. Comparative study of the psychology and behavior of homozygous and heterozygous twin pairs.
Much attention was paid to the problem of studying the individual psychological differences of children in our country in studies conducted by BM Teplov and his students. The first of these investigations were mainly aimed at establishing whether there are innate types of higher nervous activity and, if so, how they are determined. These studies experimentally tested the hypothesis that one of the inherited, genetically determined factors is the type of the human nervous system, which in turn depends on a combination of its basic properties.
The properties of the nervous system are understood as such stable qualities that are innate. These properties include:
1. The strength of the nervous system in relation to excitation, i.e. its ability to withstand for a long time, without revealing prohibitive braking, intense and often repetitive loads.
2. The strength of the nervous system in relation to inhibition, i.e. the ability to withstand prolonged and frequently repeated braking effects.
3. The balance of the nervous system in relation to excitation and inhibition, which manifests itself in the same reactivity of the nervous system in response to excitatory and inhibitory influences.
4. Lability of the nervous system, assessed by the rate of occurrence and termination of the nervous process of excitation or inhibition.
At present, a 12-dimensional classification of the properties of the human nervous system has developed in differential psychology (VD. Nebylitsyn). It includes 8 primary properties (strength, mobility, dynamism and lability in relation to excitation and inhibition) and four secondary properties (balance in these main properties). It is shown that these properties can apply to the entire nervous system (its general properties) and to individual analyzers (partial properties).
VM Rusalov further developed the ideas of the Teplov-Nebylitsyn school and proposed a three-level classification of the properties of the nervous system 1 . 1 (Rusakov V.M. Differential psychology: Main achievements and prospects for the study of human individuality // Psychological journal. - 1988. - Vol. 1. - No. 2.)
It includes:
1. General, or systemic, properties that cover the entire human brain and characterize the dynamics of its work as a whole.
2. Complex properties, manifested in the features of the work of individual "blocks" of the brain (hemispheres, frontal lobes, analyzers, anatomically and functionally separated subcortical structures, etc.).
3. The simplest, or elementary, properties correlated with the work of individual neurons.
On the basis of the studies carried out on the relationship between the properties of the human nervous system and problem solving (thinking), V.M. Rusalov came to the conclusion that only the formal-dynamic characteristics of a person’s mental activity are determined mainly (but not exclusively!) by biological factors.
Thus, the properties of the nervous system do not predetermine the mental qualities and forms of human behavior, and therefore they cannot be considered as inclinations for the development of abilities. At the same time, as B.M. Teplov wrote, they “form the ground on which some forms of behavior are easier to form, others are more difficult” 2 . 2 (Teplov B.M. The current state of the issue of the types of higher nervous activity and their definition // Psychology of individual differences: Texts. - M., 1982. - P. 25.)
Since the basic properties of the human nervous system are quite stable, the practical task of studying them in connection with the problem of individual differences is not to search for their change, but to find the best way and method for teaching children with this type of nervous system for each type of nervous system.
Developing in this regard the ideas of B.M. Teplov, V.D. Nebylitsyn suggested that a special combination of the basic properties of the nervous system, i.e. each type has its own advantages and disadvantages. In conditions of, for example, monotonous work, people with a weak type of nervous system show the best results, and when moving to work associated with large and unexpected loads, on the contrary, people with a strong nervous system.
The complex of individual-typological properties of the nervous system that a person has, first of all, determines the temperament, on which the individual style of activity further depends.
Let us now turn to a direct analysis of some facts that testify for and against the genotypic conditionality of individual differences in the cognitive processes and intellectual characteristics of children, i.e. in their assignments.
In the results of studies that were aimed at identifying the hereditary conditionality of intelligence, there is a lot of contradictory. In some cases, the connection of intellectual abilities with heredity is found, in others it is not. However, "a typical result obtained in twins on intelligence tests is that monozygotic twins are intra-paired more similar than dizygotic" 1 . "(Ravich-Shcherbo I.V. Study of the nature of individual differences by the method of twins // Psychology of individual differences: Texts. - M., 1982. -S. PO.)
At the same time, the influence of the environment on the psychology of monozygotic twins is also obvious and increases with age, while the influence of genotypic factors, on the contrary, decreases.
There are not so many psychological properties that could be considered hereditarily determined with certainty. Among the characteristics that have a clear genotypic prerequisite is, for example, the pace of a person's work, on which, in turn, temperament depends. A particularly large influence of the genotype is found in the study of certain physiological parameters, for example, an electroencephalogram.
However - and this is a very important fact - none of the known properties of the nervous system is exclusively dependent on the genotype, since it itself is influenced to a certain extent by the environment. I.V. Ravich-Shcherbo writes: “The higher the role of specifically human, voluntary speech self-regulation in an activity, the lesser the role played by genotype factors, and vice versa, the lower it is, the more clearly the individual characteristics of this activity are determined by heredity” 1 . "(Ibid.).
The data presented allow us to draw a quite definite conclusion about the absence of a pronounced biological and the presence of a distinct social conditionality of inclinations, in this case the main properties of the human nervous system, but do not remove another important issue and require its special discussion. This is a question about the genotypic conditionality of intersexual psychological and behavioral differences. There is an opinion that they are largely determined precisely by the genotype, the sexual biological identity of a person. Is this really so, and what can modern science say about this?
An analysis of the data obtained in many experimental comparative psychological studies shows that general judgments such as “Girls are better at speech than boys”, “Boys are more prone to mathematics than girls”, “Girls have a better memory than boys, but boys excel them in abstract thinking", "Girls are more passive and more sensitive to the approval of their behavior than boys", "Boys are more aggressive and more independent in their behavior than girls" are not entirely true. There are no significant differences in the level of general intellectual development between male and female children.
At the same time, there are still small age differences in the manifestation of private abilities between them. Data obtained in some studies show that between the ages of 10 and 11, girls do have a slightly larger vocabulary than boys, and they are better oriented in written texts, have a better command of the language. At the same age, boys surpass them in other respects, for example, in the ability to spatial orientation, in reading drawings, geographical maps, in geometric abilities. After the age of 13, boys develop mathematical abilities somewhat faster than girls, but not so much as to lead to significant gender differences later. At the same time, it should be borne in mind that small averaged inter-sex differences in these abilities are usually much less than those inter-individual differences that exist within the same sex.
As for personality traits, there are no noticeable differences in children of different sexes at preschool age. Intersexual differences in the early stages of ontogenesis are noticeable only in connection with one feature - external aggressiveness of behavior. In boys, it is more pronounced than in girls, starting from the age of two or three. However, this is more likely the result of gender differences in parenting practices than a consequence of biological factors.
Thus, the genotypic conditionality of the behavior and psychology of people is not confirmed in relation to gender differences. They, as we found out earlier, directly depend on education and upbringing, which, in the conditions of most cultures existing on Earth, are completely different from the very birth of a child and throughout his childhood, and so much so that we should rather be surprised by the fact that is in the psychology and behavior of men and women, not their differences.
With age, however, due to the influence of life experience and professional activities, some gender differences may increase. The data of the conducted studies show that, on average, adult men engaged in physical labor can outperform women in coordination of movements, orientation in space, understanding of mechanical technical connections, and mathematical reasoning. Women, in turn, may outperform men in manual dexterity, perceptual speed, counting, memory, verbal fluency, and other abilities that include verbal skills.
This fact is also noteworthy. Everyday experience suggests that the occupation of women by traditionally male, and men by female types of professional labor supposedly forms in them psychological characteristics that are characteristic of people of the opposite sex, i.e. lead to the masculinization of women and the feminization of men. This assumption is only partly supported by the facts. Indeed, activities traditionally characteristic of people of the opposite sex contribute to the formation and development of traits associated with these activities, but these are in fact professionally determined traits, and not those that could be considered sex-related. Such occupations, as it turned out, do not particularly affect the change in the actual sex-role forms of behavior.
Studies conducted in special, strictly controlled experimental conditions give grounds for the conclusion that socio-cultural factors associated with the development of abilities have a much stronger influence on them than biological ones. Average differences between groups of people raised in different cultures are often much larger than those between people of different sexes.
From Wikipedia, the free encyclopedia
In the case of fraternal (heterozygous) twins, each of the fetal eggs (blastocysts), after being introduced into the decidual (falling away) membrane of the uterine wall, forms its own aqueous and villous membrane, from which a separate (own) placenta with an independent network of fetal blood vessels develops for each fetus. . In this case, both placentas often remain separate. Even in cases where the edges of both placentas are closely adjacent to each other (as if merging into a single whole), nevertheless, the villous and aqueous membranes of each of the fetal eggs remain separate while they have a common capsular membrane.
Multi-egg twins (as well as identical ones) are not only twins, but also triplets, quadruplets, and so on up to 9 children. In addition, cases have been recorded when, for example, two identical (homozygous) twins and one non-identical (heterozygous in relation to the other two) twins were born in triplets.
see also
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Notes
Literature
- G. M. Savelyeva, V. I. Kulakov. Obstetrics. - M .: Medicine, 2000. - S. 816. - ISBN 5-225-04549-9
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An excerpt characterizing multi-egg twins
The next day, the troops gathered in the evening at the appointed places and marched out at night. It was an autumn night with black-purple clouds, but no rain. The ground was wet, but there was no mud, and the troops marched without noise, only the strumming of artillery was faintly audible. It was forbidden to speak loudly, smoke pipes, make fire; the horses were kept from neighing. The mystery of the enterprise increased its attractiveness. The people were having fun. Some of the columns halted, put their guns on their racks, and lay down on the cold ground, believing that they had come to the right place; some (most) columns walked all night and, obviously, went in the wrong direction.
Count Orlov Denisov with the Cossacks (the most insignificant detachment of all others) alone got to his place and at his time. This detachment stopped at the extreme edge of the forest, on the path from the village of Stromilova to Dmitrovskoye.
Before dawn, Count Orlov, who had dozed off, was awakened. They brought in a defector from the French camp. It was a Polish non-commissioned officer of Poniatowski's corps. This non-commissioned officer explained in Polish that he defected because he was offended in the service, that it would be time for him to be an officer long ago, that he is the bravest of all and therefore abandoned them and wants to punish them. He said that Murat was spending the night a mile away from them, and that if they gave him a hundred people in an escort, he would take him alive. Count Orlov Denisov consulted with his comrades. The offer was too flattering to refuse. Everyone volunteered to go, everyone advised to try. After many disputes and considerations, Major General Grekov, with two Cossack regiments, decided to go with a non-commissioned officer.
“Well, remember,” said Count Orlov Denisov to the non-commissioned officer, releasing him, “in case you lied, I will order you to be hanged like a dog, but the truth is a hundred chervonets.”
The non-commissioned officer, with a resolute look, did not answer these words, mounted on horseback and rode off with Grekov, who had quickly gathered himself. They hid in the forest. Count Orlov, shrugging from the freshness of the dawning morning, excited by what he was up to on his own responsibility, having seen Grekov off, went out of the forest and began to look around the enemy camp, which was now visible deceptively in the light of the beginning of the morning and the dying fires. To the right of Count Orlov Denisov, on an open slope, our columns should have appeared. Count Orlov looked there; but despite the fact that they would have been visible from afar, these columns were not visible. In the French camp, as it seemed to Count Orlov Denisov, and especially according to his very vigilant adjutant, they began to stir.
“Oh, really, it’s late,” said Count Orlov, looking at the camp. He suddenly, as often happens, after the person whom we believe is no longer in front of his eyes, it suddenly became completely clear and obvious to him that the non-commissioned officer was a deceiver, that he had lied and would only spoil the whole attack by the absence of these two regiments, whom he will lead God knows where. Is it possible to snatch out the commander-in-chief from such a mass of troops?
“Really, he’s lying, this rogue,” said the count.
“You can turn back,” said one of the retinue, who, like Count Orlov Denisov, felt distrust of the enterprise when he looked at the camp.
- BUT? Right?.. what do you think, or leave? Or not?
- Would you like to turn back?
- Turn back, turn back! - Count Orlov suddenly said resolutely, looking at his watch, - it will be late, it will be quite light.
And the adjutant galloped through the forest after Grekov. When Grekov returned, Count Orlov Denisov, excited by this canceled attempt, and the vain expectation of infantry columns, which all did not show up, and the proximity of the enemy (all the people of his detachment experienced the same), decided to attack.
He commanded in a whisper: "Sit down!" Divided, baptized...
- With God!
"Uraaaaa!" roared through the forest, and, one hundred after another, as if sleeping out of a bag, the Cossacks flew merrily with their darts at the ready, across the stream to the camp.
Answered by Yesenia Pavlotsky, linguist-morphologist, expert of the Institute of Philology, Mass Media and Psychology of the Novosibirsk State Pedagogical University.
The question concerns how to name and define the biological features of several organisms born from a person.
Let's begin with twins called the children of one mother, developed during one pregnancy and born as a result of one birth after a short time one after another. Such children are called twins, regardless of whether they are homozygous (identical) or heterozygous (two genetically and outwardly different children).
Twins- two twins. The nomination in this case depends on the number of fetuses in pregnancy: twins, triplets. Rarely quadruplets. Words quadruplets, quintuplets, gears and so on seem erroneous, since the language reflects reality, and in reality, a multiple pregnancy of a person is most often limited to two fetuses. Four, five, six or more twins are very rare, so the language does not seem to need a word for this object, that is, the use of such a word does not differ in frequency of reproduction.
Respectively, twins not always possible to name twins, since there can be more than two, but twins- it's always Twins: ordinary sisters, brothers or brother and sister cannot be called twins.
Despite this dictionary distinction, there is an established use of these words in another meaning.
When talking about two children born at the same time, and trying to figure out what type of twins they are talking about, people choose to separate homo- and heterozygous twins with the words twins And Twins as opposed concepts.
Homozygous twins are identical, they share the same genotype. Heterozygous twins are two different children with different genotypes that develop in different eggs at the same time. It is in order to understand what type is being discussed that people use the words twins And Twins if there are two children.
You can often hear " they are not twins but twins". That is, twins are called children who can be confused (common genotype = one appearance for two), and twins of those who were born together, but are completely different people - the same children could be born with a difference of 10 years.
The last case is not a dictionary fixation, but an established speech practice and observation of the language, so this explanation should not be taken as a rule.
So, twins not always possible to name twins, but twins- it's always Twins.
