Marriages between distant relatives. Why are consanguineous marriages dangerous?

Recent genetic research suggests that distant relatives can marry without serious risk to the offspring. Therefore, in this article we will talk about the moral aspect, religious attitude to this issue and some scientific facts of medicine.

Everyone remembers Shakespeare's Romeo and Juliet. Nowadays, love relationships between distant relatives, especially between cousins, sometimes lead to conflicts between their parents or the condemnation of others. Relatives of both families turn into Montagues and Capulets. In this article, we will find out whether relatives can marry or not, and why.

Recent genetic studies say that first cousins ​​have a 1.9% risk of having affected children. This is not a reason to call such unions a tragedy. Arno Motulski's textbook on genetics covers this topic in more detail. It is necessary to undergo the necessary consultation once again, and that’s it. Therefore, there is no need to worry.

The moral side of the issue

Many people, oddly enough, are concerned about the issue of morality. In Australia, a demonstration was held to demand the repeal of the law prohibiting marriage between cousins. Let's look at two such situations.

Brother and sister live in the same house. One apartment - one family. And the second apartment is a second family. Cousins ​​communicate and frolic every day. And they perceive each other as family. Naturally, even if they are not cousins, but fourth cousins, there can be no talk of any love.

But there is also a second option. Let's say two people live in different families. My second cousin arrived. And her brother invited her to go ice skating or gave her a free tour of the city. Sometimes there are situations when eighth grade schoolchildren come to visit their grandmother. And the three days spent together left an indelible impression. People love each other with all their hearts. But something prevents them from being close.

For some, such relationships are unacceptable, but for others they are quite natural. People decided to officially seal their relationship with the bonds of Hymen and spend the best years of their lives together. Well, we’ll talk about genetics at the end of the article. Everything seems to be going great. But many relatives, even if they are second cousins, cannot overcome the moral barrier. They are tormented by questions: “What will people say?”, “Parents will judge us,” “The Church believes that this is a sin.” Therefore, let's look at the situation from the religious side.

Church attitude

The Koran allows marriages between uncle and niece, aunt and nephew, and relationships between cousins. Previously, the Orthodox Church officially and without special rituals married cousins. But with the coming to power of communism, something changed, and it began to be considered a sin. So, the Orthodox Church in our time considers it a sin for cousins ​​to live together.

And the Catholic Church turns a blind eye to these marriages. Any certificate is suitable for marriage. And in some countries it is customary for Catholics to conduct weddings between cousins. Watch Mexican TV series. In the books “The Count of Monte Cristo” and “War and Peace,” love between cousins ​​took place.

The Protestant Church places no restrictions on relationships between cousins. Sometimes marriages between uncle and niece or between aunt and nephew are allowed. The main thing is that they love each other, and there is no bed before the wedding. However, in Protestant countries there is criminal liability for sexual relations between the closest relatives. For example, in Germany, if a brother and sister, a mother and son, or a father and daughter give birth to a child, they face up to three years in prison.

If anyone wants to approach this issue responsibly and have continuation of the family with their significant other, they are concerned about the likelihood of having sick children. Now, finally, the desire to have normal children remains.

What geneticists say

In every married couple, if they do not have common ancestors, the chance of having a sick child is from 3 to 6 percent, depending on the ecological situation of the environment. To this percentage must be added the risk of sick children as a result of the presence of common genes.

The inbreeding coefficient shows the percentage of genes that are shared. It is calculated using the following formula:

where m is the number of common relatives, n is the number of probands.

Once the coefficient of common relatedness is found, we know what the probability of common genes colliding is. And then Mendel's laws work. 25% of sick children, 50% carriers and 25% of healthy children. This means that when calculating the probability of the appearance of sick offspring, the inbreeding coefficient must be divided by another 4. Roughly speaking, the number of sick children is four times less than the inbreeding coefficient. Arm yourself with basic math and exponentiation. The carriers will never manifest themselves, so they can be neglected.

Here we are not considering incestuous marriages (father - daughter, mother - son, brother and sister having two common parents). With such marriages, inbreeding is 25%, and the probability of giving birth to a freak is about 20%. Why take the risk?

In traditional families where parents are not relatives, the risk of sick children, according to various sources, is 3 - 6%. To simplify the calculations, we assume that the possibility of a healthy baby being born is 95% (in families where the parents are not related).

Finally, let's look at a few examples.

Uncle - niece (or aunt - nephew)

The uncle's common ancestors are mom and dad (for the niece, these are grandparents). The inbreeding coefficient is 2 × (1/2) 3+1 = 1/8 = 12.5%.

Half-brothers and sisters who have only one common parent have the same indicators.

The inbreeding coefficient is (1/2) 2+1 = 1/8 = 12.5%. This means that the probability of sick offspring is the same for all such unions.

Number of sick children = 3.125% (4 times less than the inbreeding coefficient). Statistics say that the risk of disease is from 3 to 6 percent. In a word, taking into account all the necessary factors, 8 - 12% of sick children, or 88 - 92% of healthy offspring. You can have children, but you must undergo genetic testing. In further examples, the number of common ancestors is 2. And after the inbreeding coefficient is found, it must be divided by 4.

Marriage between cousins

The inbreeding coefficient is 2 × (1/2) 4+1 = 1/16 = 6.25%.

The number of sick children = 1.56% (25% if 2 common genes nevertheless collided, which is unlikely). In Japan, where cousin marriage is common in some regions, the risk of disease is only 1.9 percent. If the parents are cousins, 93% of children will be absolutely normal. There is almost no threat to your health, marry for your health.

Keep in mind that in a particular case, if parents identical twins, you can’t have children. The risk is the same as in incest marriages (20% of sick children). Well, fortunately, such cases have not yet happened. If your parents are not identical twins, Everything will be ok. A woman geneticist in the news believes that bans on marriage between cousins ​​are discrimination against ordinary people.

Cousins ​​uncle and niece

Let's consider a situation where a niece decided to marry her great uncle. Number of probands = 5 (2 generations from uncle to his grandmother and 3 generations to his niece). We calculate the inbreeding coefficient. 2 × (1/2) 5+1 = 1/32 = 3.125%. Number of sick children = 0.78%. Well, whether to go to a geneticist or not is up to you.

Second cousins

Common ancestors - great-grandparents. This means that the number of probands = 6 (3 generations from the brother to the common ancestor and 3 generations to the sister). The number of common relatives = 2. We calculate the inbreeding coefficient: 2 × (1/2) 6+1 = 1/64 = 0.0157. Number of sick children = 0.39%. That is, second cousins ​​can have children without thinking about the consequences. There is no need for genetic counseling.

P.S. So, the possibility of having a normal child is:

• Uncle and niece - from 88 to 92%;
• Cousins ​​- 93%;
• Second cousins ​​- 94.61%;
• Traditional families - 95%.

In some textbooks on genetics, the probability of sick children from marriages of a second cousin coincides with the background risks. We recommend reading textbooks by Arno Motulski and K. Stern about human genetics in your spare time.

Can love conquer all? If you don’t think for a long time, the answer to this question will definitely be romantically positive. But if we recall some historical and modern prohibitions and barriers, then the unambiguousness of such an answer may be called into question.

For example, sometimes people from different social classes simply cannot be together, and in other cases love disappears under the influence of time and distance. But there is another type of prohibition related to love and, accordingly, to marriage. This is a ban on marriage between relatives. At the same time, the greatest controversy is about the marriages of cousins. Why is this so, and are first cousin marriages really undesirable?

Why do marriages between cousins ​​cause the greatest resonance in society? Everything is very simple here. Marriages between first-degree relatives are a priori prohibited, and almost everyone agrees with this. Marriages between distant relatives, although not particularly approved, are not strongly condemned either. But marriages between cousins ​​are precisely the front line on which battles constantly take place between scientists, doctors, church workers, and, most importantly, between the relatives of those who want to enter into such a marriage.

How was it before?

History contains many facts of related marriages, and the reasons for their conclusion were very different. Some of the most significant reasons were considered political and financial. Royal dynasties previously did not allow outsiders into their circle, and marriages were concluded exclusively between persons from royal families. It is clear that there were much more ordinary people who did not belong to royal families, but the number of representatives of royal dynasties did not always make it possible to find worthy spouses without any degree of kinship.

In addition, quite often the reason for marriages between relatives was the idea of ​​some nationalities that money should not leave the family.

There were also other reasons for consanguineous marriages, such as reluctance to mix blood. Aristocratic families who were careful about the history of their surnames were distinguished by such ideas about an ideal marriage.

What do scientists say?

Now, after many hundreds of years, modern scientists say that it was marriages between relatives that became the reason for the extinction of the dynasty of the Egyptian pharaohs. After all, geneticists constantly talk about the increased likelihood of all kinds of physiological abnormalities in the descendants of those who enter into related marriages. And a clear confirmation of this, according to scientists, are the same royal dynasties, the children in which suffered much more often from hereditary anomalies and were generally less viable compared to other children born in marriages between people who do not have family ties.

In addition, in contrast to the theory about the harmfulness of mixing blood, modern scientists cite another theory, according to which the more blood is mixed, the more healthy, beautiful and mentally developed the offspring will be.

In modern society, marriages between cousins ​​are not so common. However, different nationalities have different attitudes towards this phenomenon. In many Asian countries, as well as in small settlements where residents have little interaction with the rest of society, marriages between cousins ​​are either encouraged or almost inevitable. There are no legal prohibitions on such marriages in Europe. But in America, cousins ​​cannot always officially become husband and wife, since such marriages are prohibited in 24 American states, and in another 7 states they are possible, but subject to mandatory conditions, for example, passing a genetic examination.

Marriages between cousins: possible risks

In addition to family and religious stigma, there are also certain medical risks associated with having offspring from first cousins.

These medical risks are explained very simply. The fact is that relatives are much more likely to have the same hidden gene changes. For both women and men, such a hidden gene change does not pose any danger (that’s why it’s hidden). But if such a woman and man, who have the same ancestors, think about their offspring, then the likelihood increases that their child’s gene change will not be hidden.

This is why marriages between first cousins ​​must be medically approved. Of course, it is impossible to completely exclude the possibility of the coincidence of two identically altered genes, but it is still possible to reduce the risk of genetic diseases and anomalies in the offspring. During a conversation with potential parents, geneticists carefully examine the incidence of several previous generations, establish the percentage of hereditary diseases, and also determine the nature of the relationship between a man and a woman.

Based on the results of such genetic studies, it is determined how likely it is to have offspring with genetic abnormalities.

Latest Scientific Research

Some modern scientists have ceased to be categorical about such a phenomenon as marriages between cousins. And the reason for this was scientific research, during which it turned out that the risk of genetic abnormalities in a child born from cousins ​​is only a few percent higher.

But in any case, without conducting a genetic examination, doctors do not advise cousins ​​to think about having children together.

The problem of marriages between cousins ​​affects many different aspects, both moral, spiritual and physiological. It is hardly possible to condemn people who take such a step, since this is only their choice, and no one has the right to persistently influence it. But each of us will have our own opinion on this issue, and we also have the right to it.

In modern genetics, crossing closely related individuals is called inbreeding. The higher the inbreeding coefficient, the greater the chance that recessive genes for hereditary diseases will occur. So for an uncle and niece it is 1/8, for a cousin - 1/16, for second cousins ​​- 1/32, for fourth cousins ​​- 1/64.

Even if the degree of relatedness is greater, the inbreeding coefficient will still be sufficient for a child in a pair of distant relatives to die in the womb or be born mentally retarded or physically underdeveloped. This percentage ratio and the pattern associated with it were described by Elena Leonidovna Dadali, a geneticist of the highest category, professor and author of many scientific works on genetics.

Distant kinship is also dangerous because the spouses may not even be aware of their blood ties and the presence of an unwanted recessive gene. The birth of a sick child then becomes a complete surprise and a very painful blow to the well-being of the couple. When people marry who do not have any family ties, the percentage of matches of mutant recessive genes is negligible, which is why children are born healthy.

Mutant recessive genes are a very dangerous thing, hidden from prying eyes like a time bomb. They can cause a variety of mutations, ranging from albinism and deafness to such serious illnesses as hemophilia or Tay-Sachs disease. The latter is common in some peoples of the world and is fraught with severe damage to the nervous system. A sick child never lives longer than 4 years.

As is known, representatives of the Russian royal family suffered from hemophilia. But these 2 ailments are only the tiny tip of the iceberg of hereditary diseases that can be caused by the meeting of mutant recessive genes. Only genetic analysis, which is a normal pre-wedding practice in many civilized countries of the world, can prevent it.

In the occurrence of hereditary diseases, great importance is attached to consanguineous marriages, that is, to such marriage unions when spouses have one or more common ancestors.

It has long been noted that children from these marriages will be born weaker, which is manifested in increased morbidity and mortality. Moreover, the closer the degree of relationship between the parents, the more pronounced the adverse consequences. The role of consanguinity is especially obvious when studying the pedigrees of children with relatively rare hereditary diseases. Thus, the frequency of marriages between cousins ​​in Europe and North America averages 1%, and their frequency in diseases such as albinism and ichthyosis can reach 18-53%.

The frequency of consanguineous marriages varies among the populations of different countries and regions. Thus, according to American geneticist Kurt Stern, in Brazil, the Netherlands, Sweden and the United States, the frequency of marriages between cousins ​​is relatively low and ranges from 0.4 to 0.05%. However, in a number of other countries it is still very high. For example, in India in cities it is 12.9% and in rural areas - 33.3%, in Japan - 5.03 and 16.4%, respectively.

It is known that the conclusion of consanguineous marriages is usually facilitated by economic, everyday, legal, religious, geographical, historical, etc. factors.

People have long realized the harm of consanguineous marriages, and even in ancient times there were prohibition laws. At present, in most countries and areas of the world, custom or law directly or indirectly prohibits marriage between relatives.

What is the danger of consanguineous marriages for the health of the offspring? The correct answer can be obtained by turning to genetics. It is believed that every person is a carrier of some pathological genes, i.e., in the language of geneticists, each of us, being healthy, is a heterozygous carrier of certain harmful genes. Among relatives of the same family there are many identical genes, i.e. they (although healthy) are heterozygous carriers of the same pathological gene, and therefore, during a consanguineous marriage, a meeting of two heterozygotes of the same type can occur and the birth of a child - a homozygote.

Thus, consanguineous marriages are dangerous because they sharply increase the risk of a union between two carriers of the same disease.

History shows that in some social groups, consanguineous marriages have been encouraged for centuries. Thus, the ancient Egyptians and Incas in the ruling dynasties, avoiding the “clogging” of royal blood, encouraged marriages between siblings.

It was believed that consanguineous marriages were even useful, that they could, as it were, summarize the favorable characteristics of ancestors. It is known that in some cases, inbreeding (consanguineous marriages) leads to the birth of outstanding personalities. The example usually given is the famous artist Toulouse-Lautrec, who was descended from the marriage of a cousin. The great Russian poet A.S. Pushkin was born from a related marriage.

However, humanity has more extensive information about the dangers of consanguineous marriages for human health. Numerous examples of consanguineous marriages among royal families show their harmful effects on offspring. In 1906, American researcher Adam Woods published a solid book on the inheritance of mental abilities and moral qualities among kings (“Mental and moral heredity in royalty”). He presented an analysis of the family trees of the royal houses of Hanover, Hohenzollern, Condé, Bourbon, Habsburg, and Oldenburg.

It is quite natural that many of the conclusions of an American researcher in our time sound naive. Perhaps, if Woods had had modern knowledge of genetics and medical capabilities at that time, he probably would have been able to identify something common among members of these families, such as metabolic disorders, and thereby explain such frequent disorders of the nervous system. .

In this regard, the reader may be of some interest in the pedigree of the so-called “royal porphyria”, published relatively recently - in 1968. Porphyria is a rare but severe hereditary disease with a recessive type of transmission. The basis of the disease is believed to be an increased formation of alpha-aminolevulinic acid in the body, which is accompanied by increased secretion of a special substance, porphobilinogen, in the urine (port-wine-colored urine). The disease does not manifest itself as constant, but very severe abdominal pain and nervous system disorders. The pedigree of “royal porphyria” shows that this disease was inherited in the Stuart, George (House of Hanover) and Hohenzoller dynasties. It has been suggested that this serious illness can explain some of the insane actions of Mary Stuart, the cruelty of James I and James II, the madness of George III and George IV and other monarchs.

The famous Soviet geneticist V.I. Efroimson explains this susceptibility of royal dynasties to hereditary ailments not only by consanguineous marriages, but also by the lack of natural selection.

Various national, religious, territorial and other isolation factors play a significant role in maintaining a relatively high frequency of consanguineous marriages. In this regard, the study of the health status of the population living in isolates has attracted the attention of geneticists.

Isolates include population groups that, due to various conditions (geographical, religious, social, historical, etc.) lead a separate lifestyle. Due to the small population of these groups, it can be very difficult to find a bride or groom, and marriages take place mainly within this small community. Such isolates are not uncommon; they still exist in many countries around the world. More often they arise in the Far North in the form of small settlements separated from each other by roadless areas or in the south, in mountainous or desert areas.

Currently, as part of an international biological program in many countries, scientists are conducting joint studies of the biological characteristics of different ethnic groups and isolates: in South America, the Middle East, the Hawaiian and Solomon Islands, the Eskimos of Greenland, and Alaska.

Isolates also include various socio-economic or racial strata in populous cities, wherever a group of people, part of a larger population, tends to marry only within their own circle, and this continues for many generations. For example, Jewish communities in England and Germany, Old Believers, Indians in the USA.

As we have already noted, a characteristic property of isolates is a high frequency of consanguineous marriages, or inbreeding. In isolates, the number of carriers of one “harmful” gene can reach more than 60%, and in the presence of frequent consanguineous marriages, the risk of “separation of homozygotes” becomes very high, i.e., the appearance of patients with hereditary defects. These are not theoretical calculations, these are well-known facts.

In Denmark, Sweden, Switzerland, Japan, France and other countries, examination of various isolates made it possible to detect new, previously unknown recessive mutations in humans. It turned out that the population of each isolate is characterized by its own hereditary anomalies.

Thus, genetics shows not only the social harm of caste, sectarianism, and chauvinism, but also their direct threat to human health. Economic progress, improved means of communication, increased welfare and culture, sanitary and hygienic knowledge led to the inevitable breakdown of isolates. The intensified process of migration and urbanization of the population leads to a significant reduction in isolation factors and the frequency of consanguineous marriages. Scientists say that the number of mixed marriages is constantly increasing, and this reduces the incidence of hereditary diseases.

Marriages between relatives are not approved by religion and science. This is explained by the fact that there is a very high risk of having defective children.

Despite this, history contains many facts of marriages between relatives. They were not always concluded out of love and consent. There were financial and geopolitical reasons for this.

Marriages between relatives is an issue that does not lose its relevance in the modern world.

In medicine, marriages between relatives are called inbred, which means a union between persons of the opposite sex who have at least one common ancestor.

Often there is such a term as incest - the entry into intimate relations of close relatives, mixing of blood.

History describes tribes in which, in order to preserve the purity of the family, it was customary to marry relatives. As a result, they have almost all disappeared or are on the verge of extinction.

Nowadays, in many countries of the world, marriages between blood relatives based on a certain degree of relationship are not only condemned, but also prohibited by law and equated to a criminal offense. This is explained by physical and moral considerations.

In Russian legislation, there is Article 14 of the Family Code, which does not allow marriage between persons who are related in an ascending or descending line:

• parents and children;
• grandparents and grandchildren;
• brothers and sisters;
• adoptive parents and adopted children.

Despite this, the registry office does not require documentary confirmation or refutation of family ties. Marriage between relatives of the adoptive parent and adopted children is permitted.

In addition, Russian laws do not prevent the creation of a family between:

• uncle and niece;
• aunt and nephew;
• cousins.

This is condemned by society, but is not formally prohibited, which means you can marry such relatives.

At the insistence of genetic scientists, marriages between blood relatives are prohibited at the legislative level.

The Family Code of the Russian Federation also does not allow marriage between blood relatives, under any circumstances.

In this case, the basis for registering a marriage is not even the woman’s pregnancy.

In fact, marriages between relatives can be registered. After all, when submitting an application to the registry office, newlyweds are not required to confirm or deny the existing relationship.

If a couple hides the fact of their relationship, the marriage will be registered, but then it may be declared invalid.

Marriages between adoptive parents and adopted children are only allowed if the adoption is cancelled.

Marriage between closest relatives is considered incest.. But it is worth considering what genetics says about marriage between a second cousin.

Such family ties are considered distant. Marriages between them are possible and quite common, especially in Muslim countries.

The risk of having a child with anomalies from such a union is quite low. There are chances that a full-fledged baby will be born.

The problem with consanguineous marriage is the possibility of spouses carrying mutagenic genes in a latent state.

It is almost impossible to determine which genes these are. It is also unrealistic to predict exactly what abnormalities may appear in a child.

The risk increases that a woman will not be able to bear the fetus, as well as its fading. Therefore, it is difficult to determine how pregnancy will proceed in a related marriage.

A blood test for HLA antigens helps to assess the genetic similarity of spouses.

During pregnancy, specific diagnostics regarding consanguineous marriage are not carried out.

In 2019, a standard ultrasound and triple test are performed to exclude gross anomalies of fetal development.

For decades, there has been an opinion that the closer the parents are by blood, the more negative the consequences of having children in a consanguineous marriage will be, so they are not desirable.

We are talking about serious vices:

• hemophilia;
• Down syndrome;
• dementia and other pathologies of the nervous system.

Offspring from consanguineous marriages may be mentally and physically weaker.

In an ordinary marriage, the probability of having children with genetic defects and mental retardation is 4%.

In a closely related marriage, the risk increases 5 times.

Science has long proven that intimate relationships between relatives are dangerous to the health of their offspring. Children born from direct relatives can suffer from a number of the most dangerous diseases.

Marriage between first cousins ​​is not considered a consanguineous relationship..

But according to genetics, in such a marriage compared to unrelated ones, the following increases:

1. The risk of stillbirth or intrauterine fetal death is 24%.
2. The risk of a child dying at an early age is 34%.
3. The risk of developing fetal deformities is 48%.

In addition, geneticists have identified a stable pattern in the frequency of diseases, congenital deformities, mental and physical disabilities in children born as a result of consanguineous marriages.

This point of view on this issue is shared by experts in many countries.

When studying hereditary diseases, much attention is paid to consanguineous marriages. In the case where the parents have at least one common ancestor.

Incest plays an important role in the study of rare blood diseases.

As for marriages between relatives, most often disputes arise specifically over marriages between cousins.

Everything is explained very simply - marriages between persons of the first degree of kinship are prohibited, almost everyone agrees with this. Marriages between distant relatives are not prohibited and do not cause special condemnation.

But marriages between cousins ​​cause a lot of disagreement between scientists, doctors, church ministers and between relatives of those who want to enter into such a union.

Marriages between cousins ​​were for a long time under a moral prohibition. And in many states of America they are outlawed.

But the theory of genetic incompatibility, which became the basis of such beliefs, does not find scientific evidence.

In the modern world, the scientific community is fighting for the right of everyone to register a marriage with a loved one.

Cousins ​​can marry; this is not legally prohibited.

British researchers have come to the conclusion that all laws that prohibit such marriages are a legitimate form of genetic and sexual discrimination.

Researchers have spent a long time studying modern statistics and historical data and have come to the unequivocal conclusion that children born in marriage between first cousins ​​have the same chances of birth defects and genetic diseases as any other babies.

Scientists attribute the ban on such families to social rather than genetic factors.

The likelihood of developing hereditary diseases in marriages of first cousins ​​is approximately 2% higher than in marriages of non-relatives. If you have common ancestors, the risk of carrying the altered gene increases.

If both parents have such a gene, then together with a healthy gene, the chance of the diseased gene appearing is 25%. When two altered genes are found in a couple, the risk that the children in such a marriage will have anomalies is 50%.

The accuracy of the forecast depends on how complete the information about the pedigrees is. It is important to have data on the number of relatives, hereditary diseases and the development of defects in them.

But in any case, without a genetic examination, medical professionals do not advise cousins ​​to think about having children together.

The problem of marriage between cousins ​​affects moral, spiritual and physiological aspects. Each person has the right to make his own choice and no one has the right to influence him.

Starting a family is one of the main stages in the life of mankind. In Russia, as in all civilized countries, marriage between close relatives is considered illegal.

Article 14 of the Family Code of the Russian Federation outlines a direct prohibition on marriage between persons who are closely related.

But there are no legal obstacles to creating families between brothers and sisters who do not have common parents - first and second cousins. Therefore, marriage between such relatives is possible.