Genes and environment: what twins can tell us about the fate

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© Maja Daniels

Heredity or environment, surrounding atmosphere or natural inclination — what makes us what we are? Find the rational arguments in this debate help for the psychological study of identical twins. From birth they have the same set of genes, and therefore any differences between them, whether it be homosexuality, IQ level, or religiosity, can be attributed to the influence of environment and education.

"For the existentialist man is not, therefore, be easily ascertained that the original is nothing. Man it is only later, and as he'll do himself." These are the words Jean-Paul Sartre. I wonder what would have objected to the French philosopher twins Jim Springer and Jim Lewis, separated in childhood and so mysteriously accurately recounted the fate of each other.

For the first time after the birth of the brothers was found at the age of 39 years. By the time they have time to grow smoothly up to 6 ft (1 m 82 cm) and score at 180 lbs (81 kg) weight; get same name from his foster parents and called their dogs Toy and their firstborn James Alan; to marry women named Linda, then divorced and married a second time; stick to work on wood, cigarettes, "Salem" and rest on the same Florida resort. And Jim Springer and Jim Lewis were both sheriffs, hated baseball, suffered severe headaches and gritted his teeth at night. They lived 100 miles away from each other. It seems that their fate was predetermined.

Twins and intelligence: the first issledovaniyeyami or monozygotic (MZ) twins are born when a sperm fertilized the egg during its development is divided into two parts. They are always the same sex and have identical genes. In contrast, dz (DZ) twins can be different genders, and their genotypes are not more than ordinary brothers and sisters, — only 50%. These children develop from two different eggs fertilized by two sperm at about the same time.

If you take, for example, 100 pairs of siblings, duagava 100 pairs of twins and 100 pairs of identical and in pairs to compare their height, weight or IQ, we can obtain an estimate of contribution of heredity and environment in the development of each of these signs (MZ twins have the same genotype, and born at the same time, grow in the same conditions. DZ twins are also growing in the same conditions, but differ in genotype. And, finally, ordinary brothers or sisters can not boast of neither one nor the other).

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However, a pilot scheme, twin studies differ from those described. So, scientists particularly appreciate the cases of separated monozygotic twins. The first such study appeared in 1937. It, along with raised together, MZ and DZ-twins were studied 19 pairs of separated MZ twins. All subjects passed a few intellectual and psychological tests, the results of which showed that even separated identical twins are more alike than fraternal (although still not as much as identical twins raised together).

Similar conclusions, suggesting that intellectual development is rather determined by genes and not environment, it has turned out in much larger Louisville twin study, which took place in America from 1957 to the mid-80s. For 30 years, it was attended by about 500 pairs of twins who were tested from birth until the age of 15 — and again it turned out that MZ twins are much more similar in intellectual development than DZ twins.

The results of this study and almost a hundred other papers summarized the American psychologist Thomas Bouchard, who showed that the heritability of intelligence varies greatly with age. And if in childhood IQ of MZ twins (or IQ normal IQ children and their parents) can still differ markedly, with age, this difference is gradually disappearing. Genes, it turns out, as if you are looking for the best environment for their development.

Twins and homosexuality: the vicissitudes metodikoi twin studies have been conducted in the Soviet Union. So, in 1936, there appeared a paper (A. R. Luria, Mironova A. N.), devoted to the evaluation of different teaching methods. The subjects of the five pairs of identical twins of preschool age were divided into two groups, each of which got only one child of the couple. Then the kids built things out of blocks. The twins are the first group simply copied the designs that they offered carers and their siblings were more complicated: their figures were covered with paper. Therefore, to reproduce the designs they had at first thought to cut and perform.

This training lasted two and a half months. To his design abilities in all twins pairs was estimated to be approximately the same, but after children, carrying out more complex and creative task, well ahead of their partners.

But should we trust this study? Five pairs of subjects is a very small sample by the standards of modern science. Unfortunately, this limitation is a characteristic of many twin studies conducted up to 90 years to gather enough data to obtain statistically reliable results without the use of the same e-mail was not easy.

However doubtful may be the results of larger studies. So, in 1952 published an article by American scientists, which told of the absolute coincidence of the sexual orientation of MZ-twins. The results are impressive — it turns out that nature and heredity to a much greater extent, homosexuality, culture or propaganda.

Article 1991 corrected this figure: in this study, survey respondents and their relatives were identified sexual orientation 56 pairs of MZ twins, 54 pairs of DZ twins of male, 142 siblings and 57 pairs of adoptive brothers. As a result, homosexuals were 52% of identical twins, 22% duagava, 11% of adoptive brothers and 9.2% for siblings — again, clear evidence of genetic differences of homosexuality (the results of more recent research with a female sample showed similar results). But only where such large numbers? So many gay men you can meet except in American films and television series. And the results with natural and adopted brothers contrary to the global hypothesis: sexual orientation is genetically identical to 50% of siblings have to match much more often than brothers foster, who was just brought up together.

It turned out, it's all in the ways in which experimenters found their subjects: for this article in 1991, scientists placed an ad in the gay press, and a study of 1952 and did was almost entirely carried out on patients in psychiatric hospitals.

More careful twin study of sexual orientation was published in 1992. It was attended by 46 homosexual men and women — identical twins. As a result of their sexual orientation coincided with the sexual orientation of brothers and sisters only 10%/25% chance for MZ twins and 8%/12% for DZ twins (higher values were obtained if together with the account of the homosexuals and bisexuals).

Gemini and health: from obesity to autism.practice myself that the human body is a sheet, which is suspended on elastic bands stretching from hooks on the ceiling. This metaphor offers the famous evolutionary biologist Richard Dawkins to understand the intricacies of genetics and the environment determine all of our traits, like musical talent, inclination to depression or even disposition to the dairy food.

Here the hooks are genes, and gum — their impact on the symptom. Some genes are passive and just stick the old memory from the ceiling. Apparently, they were needed by our ancestors. From the active to the sheet stretch bands that can shrink/stretch, (the gene is used more often/less often), or even curl (gene mutated) — all of these changes will affect the sheet. They will affect not only attached to the gum area, but the entire system: other pieces of fabric (the other traits of an organism), other bands from this hook (the activity of this gene in other parts of the body) and even gum other hooks (the activity of other genes).

So what about the "genius genes" or "genes have a drinking problem", the eternal heroes of news headlines, with this picture you can forget. Even hung with hundreds of rubber bands, the hook can not alone determine some property sheets like twist clockwise. But where is the environment? Where is the power of a person or his social circle? View, says Dawkins, our bed sheet hangs from the ceiling of the room, and from the Windows it attracted the rope from the neighboring trees and houses. This is the influence of the environment.

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To analyze for each individual external sign of the body, these intricacies is a very difficult, if not impossible. Therefore, in genetic studies (including twin) consider a generalized numerical characterization of the heritability, the value of which ranges from 0 (the variability of the trait in the population caused by the influence of the environment) to 1 (fully variability caused by differences in the genotype).

In addition, heritability can change over time or depending on many other parameters. Thus, the twin study by Finnish scientists in 2008 showed that the heritability of body mass index (ratio of weight in kilograms to the square of the height in meters) decreased with increasing physical activity (to confirm an old truth: the more one moves, the less chances he has to inherit the extra weight or, on the contrary, the painful thinness of his parents).

In a study of 2011 already studied the heritability of autism. It was attended by almost 200 pairs of MZ and DZ twins in which at least one partner was discovered autism spectrum disorder. It turned out that identical twins are much more likely to suffer these mental disorders than fraternal, but the heritability of autism ranges from 0.7 to 0.9.

Gemini and the consciousness of telepathy to религиозности8-year-old Richard sound-transparent Polsa close in the room and put in front of a bucket of ice water. Through the wall — his brother Damian, hung with sensors to monitor heart rate, respiration and electrical activity of the skin. The researcher gives the signal. Richard lowers his hands into the bucket. Deep breath. All the sensors are going wild. Damian feels the shock of his brother.

In these stories telepathically linked identical twins can not believe it, but the fact that they are much better than ordinary brothers and sisters understand each other, noticed still long ago. Often twins, even it is difficult to build an independent identity. Especially when from childhood dressed in the same clothes. In addition, twin studies Jenny van Dongen show high genetic predetermination of the many characteristics of the brain. Thus, the heritability of brain volumes is equal to 0,66–0,97, and his frontal lobes and is 0,90–0,95 (though the heritability of the volume of the hypothalamus is much smaller: 0,40–0,69).

These formal characteristics are genetically identical MZ twins should have very similar minds. Maybe this may explain such a strange coincidence in their lives, like the love of one brand of beer or divorces with their spouses. In any case, the contribution of genes, calculated again on twin studies, in certain "signs" that seemingly always lying in the plane of the "my free will and the influence of others," is quite high: the heritability of Smoking for men is 0,59, have a drinking problem — changes in the range of 0.5–0.7, and love to exercise, respectively, from 0.48 to 0.71.

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© Ariko Inaoka

Work 2005 the twins studied the propensity towards religion. The study involved 169 pairs of DZ - and 104 pairs of MZ twins. Since childhood and for many years they were asked how often they go to Church, pray or discuss religious topics. In addition, the researchers asked the twins the same questions about their closest relatives — how often, in their opinion, going to Church, praying mother or brother. It turned out that in childhood almost all subjects believed in the religious unity of his family. Then the picture changed — fraternal twins worse knew their relatives, and all differed in religious views. But the twins, by contrast, continued to give similar answers, as if the faith is almost certainly written in their identical genomes.

Gemini and constancy: gender and голос5 may 2004 David Rayner, 40-year-old canadian from Ottawa, the father of three adopted children, shoots himself in the head with a shotgun. A few months earlier from an overdose of antidepressants dies of his twin brother Brian, and for 39 years before David did and botched circumcision burned the penis electric shock. But then he was still Bruce.

After surgery, the hapless parents decided to make Bruce the girl Brand. They found him a doctor who was convinced that gender is influenced by environmental, testicles were removed and bought a lot of pink clothes. But in 11 years of Brand refused the surgery on the formation of female genitals, and at 13 she learns the truth. Brand three times trying to commit suicide, but survives. Hormones and the next operation is helping her to transform back into a man.

In 2000, David Rayner, the former Brenda, Bruce, former and future suicide told his story to the world. Turns out he's childhood suffered from feelings of discrepancy with himself. Didn't want to take hormones. Do not play with the dolls. Not interested in boys. Genes knew exactly who he really is.

But even after such stories, you can still argue that more defines gender identity — nature or environment. But with our votes everything is much uniquely. They seem almost completely determined by genes.

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In 2001, researchers from Belgium conducted a test in which they were proposed to choose among the three voice recordings of two MZ twins. If such a selection was done randomly, then the probability of success was 33% (one out of three people you can make three different pairs, one of them is a pair of twins), but in the experiment, people guessed the twins-twins of men and women in 82% and 63%, respectively.

Later another Belgian group conducted another study. Scientists took 45 pairs of identical twins, recorded their voices and then analyzes this information: determined by the upper frequency of a sound, its intensity, and even cleanliness. As a result, almost all the parameters of the voice of MZ twins were very close to each other (some deviations were observed only in women or subjects under the age of 17 years).

The twins and chance: epigenetically amendment to all of the previous text: even the genomes of identical twins differ from each other, and it is not in mutations. Quite small, sometimes random, changes in the conditions of the intrauterine environment and child development will go some other way. Some genes are activated, while others will stop working. One rubber band will tighten, the other will go to the folds, and the third and tear at all. So voles are born in the spring with the usual wool and fall long and thick. So useful in anticipation of cold development of the body the other way runs a small variation in the concentration of melatonin, the hormone of "internal clock" in the mother's blood.

Such changes, like breaking the eternal dichotomy of "heredity — environment", referred to as epigenetic. The fact that the genome Assembly instructions for synthesis of all proteins the body needs — never used completely. Moreover, different cells of the body utilize it in different ways. Genes whose proteins are not needed in this place and at this time, can be blocked by reversible chemical reactions. They change the "external" structure of the gene, making it impossible for protein synthesis, but retain the structure of the "internal" — a sequence of nucleotides encoding part of the protein.

A large study on the genetics of MZ twins, appeared in 2005. It turned out that their epigenomes differ from birth, and with age, this difference increases. And the more time the twins live separately from each other. But what causes these changes? All the same, that is determined by genes, — the habit of exercise, and Smoking, diet and alcohol. The eternal cycle of the environment and heredity, run by the blind accidents.  published 




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