En el vientre materno. Gemelos idénticos. Documental
Los gemelos son lo más parecido a la clonación que existe en la naturaleza, su configuración genética idéntica es una de las maravillas de la reprodcción humana. Las similitudes causan estupefacción, incluso los gemelos idénticos separados al nacimiento llevan vidas sorprendentemente similares pero los gemelos idénticos también contradicen las espectativas, los avances en la genética revelan que los gemelos idénticos no son tan iguales como pensamos.
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00:00Here's your babies in 4D, and as we can see, they're identical.
00:22Twins are the closest thing to human cloning in nature.
00:28Their identical genetic configuration is one of the wonders of human reproduction.
00:36Similarities cause stupefaction.
00:40Even identical twins separated after birth usually lead surprisingly similar lives,
00:46with the same jobs, tastes and hobbies.
00:53But identical twins also contradict expectations.
00:59Genetic advances reveal that twins are not as similar as we thought.
01:11Thanks to the latest technology in 4D micrography,
01:15to visual effects of scientific accuracy,
01:18and to microscopic images,
01:20we'll be able to show you what's hidden in the world of twin fetal development.
01:33In the mother's womb, identical twins.
01:47In a world where most of us are individual beings,
01:50the existence of identical twins excites the imagination.
01:56But for scientists, the most fascinating thing is not their similarities,
02:01but their differences.
02:04Even if they don't look like it, these two children are identical twins,
02:08although they were born with great weight differences.
02:17Twins like these, with great physiological differences,
02:20are a great opportunity to reveal the truth about human identity.
02:29From fingerprints and intelligence,
02:32to diseases, and even sexual orientation.
02:47Like all of us, the life of twins begins in a single cell.
02:54A fertilized egg called the zygote.
03:03This cell contains 23 pairs of chromosomes.
03:06In other words, chains of genes.
03:09One from the mother, and one from the father.
03:14Together, both configure the genetic plan of the new human being.
03:24Day 1.
03:29A few hours after fertilization,
03:31the cell with its load of chromosomes begins an extraordinary journey.
03:39First, it moves to the uterus along the fallopian tube.
03:43Then it begins to subdivide.
03:46First in two, then in four, then in eight.
03:51Each one is an identical replica of the others.
03:56This set of cells, which multiply at high speed,
03:59is called the blastocyte.
04:02This is where the most surprising reproductive anomaly occurs.
04:12In an exceptional way, something so mysterious happens
04:15that until recently, it had never been witnessed.
04:22A few days after conception,
04:24the blastocyte splits in two spontaneously.
04:33Each blastocyte is made up of cells
04:35that have an identical set of chromosomes
04:39that carry the same genetic configuration.
04:43Both blastocytes are potentially susceptible
04:46to becoming identical twins.
04:56Exactly how and why the blastocyte splits
04:59is one of the greatest mysteries of reproductive science.
05:03However, during a laboratory study carried out with 26 embryos,
05:08experts were able to observe this phenomenon for the first time.
05:14The outer membrane of the blastocyte is called the pellucid zone.
05:19The interior of this layer is known as the trophoblast,
05:23a film made up of a single row of cells
05:26that will later transform into the placenta.
05:31Inside, there is the inner cellular mass.
05:34The embryonic stem cells will give way to the fetus.
05:41Embryologists realized that for four days,
05:45the bond that connected a cell to the trophoblast was weakening,
05:51allowing the trophoblast to disintegrate
05:54as if it were a balloon full of water,
05:56due to the release of liquid.
05:59Later, the trophoblast regenerated.
06:05But the embryologists found two ovules
06:08in which something they had never seen before was occurring.
06:13When the membrane was deflated,
06:15the inner cellular mass was divided into two.
06:19Each part adhered to an area of the trophoblast and reinflated on its own.
06:27If each part developed inside a uterus,
06:30they would grow to become identical twins.
06:38When the fertilized ovule is born,
06:41it is not surprising that most identical twins
06:44retain a similar physical appearance as they grow.
06:48Genetic influence goes beyond what we see.
06:52Genes also affect personality and tastes,
06:55making us extroverted and not shy,
06:58more coffee-loving than tea-loving,
07:01inclined to routine,
07:02or eager to try new things.
07:08The similarities between twins are more than a matter of skin.
07:15Dennis and David Herrera are a pair of 53-year-old identical Californian twins.
07:22After studying at the institute,
07:24they both became agents at the Los Angeles Department of Police.
07:28Since they grew up together,
07:30attended the same school,
07:31and had the same friends,
07:33it is impossible to elucidate whether their choice of profession
07:36was the result of genetic influence or the environment.
07:46To truly test the intensity of genetic influence in our lives,
07:50scientists study identical twins
07:53separated after birth and raised in different environments.
08:01Daphne and Barbara were separated when they were babies,
08:04and for 40 years they had no contact with each other.
08:10They were raised in very different families,
08:13one in the home of a scientist,
08:15and the other with a municipal gardener.
08:19Despite this, the similarity between the two is striking,
08:23and perhaps more than a coincidence.
08:26Both left school at 14 and fell in love at 16.
08:33Before turning 25,
08:36they had married their first boyfriends.
08:40At the same age,
08:41the two suffered spontaneous abortions,
08:43but continued to have children.
08:47Both exhibit an irrational fear of blood and falls.
08:55When they met at the platform of a railway station,
08:58they were dressed almost identically.
09:04The similarities are remarkable,
09:06which suggests that genes play an important role
09:09in the development of our lives and personalities.
09:17But as we will see below,
09:19it is the differences between the identical twins
09:21that provide the greatest opportunities
09:23to solve a debate as old as history,
09:26nature or the environment.
09:31When these twins were born in 2006,
09:33Jake weighed about two and a half kilos.
09:38Tom, his twin brother,
09:39only weighed a little over half a kilo.
09:43Since they are identical twins,
09:44this great difference was mysterious.
09:48To solve the riddle,
09:50the doctors investigated the environment
09:52they had shared before birth,
09:54the uterus.
10:01Day 5
10:04Five days after fertilization,
10:06the two identical twins have reached the uterus.
10:09Here they will have to face the most important events
10:12of their nine-month odyssey,
10:14events that will have a spectacular impact
10:17on their existence inside and outside the uterus.
10:21When they were born, Jake weighed two and a half kilos,
10:24and his brother Tom only half a kilo.
10:30This despite being identical twins
10:32born with a difference of minutes.
10:39How is it possible that two twins
10:40with the same genes seem so different?
10:45The answer could be found not in their DNA,
10:48but in the events that occurred
10:51in the environment they shared before birth,
10:53the uterus.
10:56The first and most important is the implantation.
11:06Day 6
11:08Around the sixth day,
11:09the blastocyst must be implanted in the wall of the uterus
11:12to ensure its position
11:13during the next 250 days of gestation.
11:18The opportunity is everything.
11:23Each twin will depend on a placenta
11:25that will provide oxygen and nutrients.
11:28However, the placenta begins to develop
11:31after the implantation.
11:33This means that the blastocysts
11:34that break before the implant
11:36each have their own placenta.
11:39However, those who do it later
11:41must share the same placenta.
11:47As a result,
11:49one of the twins will receive less food than the other.
11:54The result is that one of them will grow much less,
11:57a circumstance known as
12:00intrauterine growth restriction.
12:10There are even some rare cases of identical twins
12:13who suffer from this condition,
12:15even though they have their own placenta.
12:18This is what happened to Jake and Tom.
12:25Their weight differences are the result of something
12:28that happened long before they were born,
12:30although their effects will be felt for the rest of their lives.
12:42THREE WEEKS
12:45Once the implantation has taken place,
12:47embryonic development is surprisingly fast.
12:53At the end of the third week,
12:55a form with the appearance of a rudimentary body emerges.
13:05At that moment,
13:06the embryo looks like a body without skin or bones.
13:13The mother cells flow from one end.
13:16Its fate is dictated by the organiser.
13:19One of the first organs to form is the heart,
13:23which until now was just a set of muscle cells.
13:28Then, around the 22nd,
13:30a cell that is part of this dormant agglomeration
13:33contracts spontaneously.
13:40This movement produces a chain reaction.
13:46One after the other,
13:47the rest of the cells around it contract
13:50until the whole group starts beating.
14:08Two tiny hearts the size of pinheads
14:11start beating together.
14:29Our tiny embryos have approximately the same number of cells
14:33and the same DNA.
14:35Although it may seem incredible,
14:37at this point they could be different.
14:43Is personality an innate characteristic
14:45or something we learn over time?
14:48Why are some of us victims of diseases
14:51while others remain immune to them?
14:55Where does the colour of the skin come from?
14:57What makes one person homosexual and the other heterosexual?
15:03The answers are not as simple as we thought.
15:11Remy and Kian are twin brothers.
15:17The result of the fertilisation of two different eggs
15:20by different spermatozoa.
15:26The girls' parents are of mixed racial origin,
15:30which means that their children will also look like them.
15:34But that's not always the case.
15:38The mixed racial origin
15:40involves the carrier of genes for both light and dark skin.
15:45In Remy's case,
15:47a spermatozoa that had the gene that produces dark skin
15:50fertilised an egg with similar characteristics.
15:56In Kian's case,
15:58a spermatozoa that had the gene that produces light skin
16:01fertilised an egg with the same gene.
16:07The result?
16:09Twin sisters of very different looks.
16:14Remy and Kian show us that twins can contradict expectations,
16:19but they are not the only ones.
16:25In 2001, a pair of twins were born
16:27that at first looked like a boy and a girl.
16:32A closer examination revealed that one of them
16:35had both male and female sexual organs.
16:40It was a hermaphrodite.
16:43Scientists believe that this happened because the same egg
16:46was fertilised by two spermatozoa,
16:48one with male sexual chromosomes and the other with female ones.
16:54The egg became a blastocyte with cells of both sexes.
17:03When it was subdivided, each cell had an extra chromosome,
17:07which gave rise to a blastocyte with male and female cells.
17:18Then the blastocyte started to create twins.
17:23Coincidentally, one of them had more chromosomes of the male sex
17:27and gave birth to a boy.
17:29While the other one had the same number of cells
17:32with male and female chromosomes,
17:34which produced a baby with genitals of both sexes.
17:40An almost incredible discovery.
17:43Twins halfway between fraternals and identical twins.
17:48It is the only case where semi-identical twins are known.
17:52The simple classification that we used to use comes down,
17:55helping us to understand how twins,
17:58and by extension the rest of us, develop.
18:08Five weeks.
18:10In the fifth week, our embryos of identical twins
18:13begin to take shape.
18:22Curved in the shape of a C,
18:24their heads and tails can be distinguished.
18:29The same as the hearts,
18:31the spine,
18:33and the beginnings of small limbs.
18:43In this phase, the human embryo hardly differs
18:46from the rest of the vertebrates.
18:50These fragile creatures,
18:52which only measure a millimeter and a half,
18:55are about to enter a critical period,
18:57the cerebral development.
19:07This event, which takes place in the fifth week,
19:10could be another crucial moment
19:12in the development of the differences
19:14between identical twins before their birth.
19:19Celso and Jesus Cárdenas
19:21are identical twins who were raised together.
19:28As they grew up, their physical appearance was similar,
19:31although their tastes and interests were differentiated.
19:35Celso was interested in dance and the academic world,
19:39while Jesus preferred sports.
19:43The most surprising difference between the two brothers
19:46is that Celso, who is dressed in black, is gay.
19:53The difference in sexual orientation
19:55between identical twins
19:57is an opportunity to investigate
19:59one of the most controversial questions in science.
20:02Are homosexuals born that way?
20:09Since Celso and Jesus grew up with the same parents
20:12and in the same home,
20:14it is inevitable that they share the same environment
20:17at the crucial moments of their personal development.
20:25In the general population,
20:27the probability of being gay is less than 5%,
20:31unless your twin brother is.
20:34In this case, the probabilities are much higher.
20:38In the case of twins,
20:40the so-called fraternal twins,
20:42who share half the genes,
20:44the probability that, being one gay,
20:46the other is also gay, is 20%.
20:50This proportion goes up to 50%
20:53when they are identical twins,
20:55those who share all their genes.
21:01This indicates that our sexuality
21:03must have some genetic component.
21:12However, not everything is a result of the genes.
21:16If it were, all twins would be either heterosexual or gay.
21:21There must be other factors.
21:33During their first weeks,
21:35all fetuses develop in the same way.
21:38If nothing changed, we would all be females.
21:43But in the sixth week,
21:45the fetuses with the male chromosome Y
21:48begin to develop testicles,
21:50which produce a hormone called testosterone.
21:56During the eighth week,
21:58testosterone spreads and can affect the development of the brain.
22:02This hormone masculinizes the body
22:04and can also masculinize the brain,
22:07including a part of it known as the hypothalamus,
22:10which is part of the network that controls
22:12what we find sexually attractive.
22:18Some scientists believe
22:20that the more exposed the hypothalamus is to testosterone,
22:23the more likely the new human being will be
22:26to feel inclined towards women.
22:32Sometimes, the male fetus may not produce enough testosterone
22:37or his brain may not absorb enough testosterone
22:40to become heterosexual.
22:44If this theory is true,
22:46then it could be that Celso, the gay brother,
22:49would have absorbed enough testosterone to masculinize his body,
22:53but not enough to completely differentiate his brain.
22:57The result of this is attraction by men.
23:07Although there are still many questions,
23:09twins like these are playing a crucial role
23:12in helping scientists find out
23:14how and when we all develop our sexuality.
23:22In the eighth week,
23:24our identical twins have completed their embryonic development phase.
23:29It is now when they are known as fetuses,
23:32which comes from the Latin word that means baby.
23:35They are safe inside their own bags,
23:38although they share the placenta.
23:40The twins still have about 200 days left until they are born.
23:45The growth begins to accelerate.
23:51Thirteen weeks.
23:52Around the thirteenth week,
23:54the fetuses begin to appear more human.
24:00The eyes are getting closer.
24:03And the proportion of the head with the rest of the body is improving.
24:13It is the end of the first quarter,
24:15a time when most pregnant women
24:18undergo their first ultrasound.
24:27The ultrasound sonographer examines the basic indicators of normal development.
24:32Here's your babies in 3D.
24:34As we can see, they're identical.
24:43The sonographer observes a single placenta,
24:46a clear indication that they are identical twins.
24:49You can see here a single placenta cut transversally,
24:53which proves that they are identical twins.
24:56So when will we see them start interacting or reacting to one another?
25:00Now we can almost see them moving.
25:07From now on, the mother will be closely followed.
25:12Twin pregnancies have a higher risk of premature birth.
25:18The incomplete development of the lungs and other organs
25:21can lead to complications that endanger natural birth.
25:26As a result, twin mothers have a 50% higher chance of needing a cesarean section.
25:40The ultrasound marks the beginning of the second quarter,
25:46which extends between weeks 12 and 24.
25:51During this period, not only will there be enormous growth,
25:55but also a remarkable development of the entire body,
25:58from the structure of the brain to the refinement of the facial features.
26:03At the end of this period, the fetuses will still be small,
26:07but they will be almost perfectly formed.
26:15They seem very similar, but recent research
26:18reveals that even at this stage,
26:21identical twins may be less than what they seem.
26:26Some changes are taking place that will increase throughout their lives.
26:34The responsible mechanism is one of the most complex and fascinating processes
26:38of all human development.
26:49FIFTEEN WEEKS
26:53Fifteen weeks.
26:57In week 15 of their journey from conception to birth,
27:00our identical twins begin to move for the first time.
27:09They begin to interact by exploring their surroundings with their hands and feet,
27:13touching and looking as if they were kissing.
27:19Later, their mother will feel the kicks of each of them in the uterus.
27:28Sometimes they seem aggressive, others almost affectionate.
27:34Although they seem identical at first glance,
27:37perhaps some invisible influences may be affecting them.
27:41Some influences that could alter in a subtle way
27:44the way the genes will manifest within their bodies.
27:53The identical twins, Jake and Tom, are seven months old.
27:59Jake is eight centimeters taller than Tom,
28:02and four kilos heavier than him.
28:09When they were born in 2006,
28:12doctors attributed the differences to a lower level of nutrition in one of them
28:16due to the differences in blood flow in the uterus.
28:21They hoped that Tom would reach his brother,
28:24but a year and a half later they are studying
28:27if Tom suffers from a congenital disorder called Russell syndrome,
28:31which produces a deficient growth.
28:36One of the causes of the syndrome is a problem in the gene of growth
28:40located in chromosome 11.
28:45Scientists find it strange that only one of the twins suffers from this syndrome.
28:52After all, identical twins have the same genes.
29:03Genetic puzzles like this one are opening the way to an unknown world
29:07located within the limits of science,
29:10epigenetics.
29:14This field of biology, which is currently in the growth phase,
29:18could explain the differences between twins like Tom and Jake.
29:25This discipline has been used to find out that their DNA code may be the same,
29:30but not their functioning.
29:34The human genome contains around 27,000 genes,
29:38each with its own specific function,
29:41such as the production of energy or the direction of cellular subdivision.
29:45Now geneticists are studying an aspect previously unknown to the genome,
29:50the epigenome.
29:54There is a whole series of chemical products that act as switches
29:58capable of activating or deactivating certain genes.
30:03One of them works through a process called DNA methylation,
30:09by which the enzymes found inside a cell
30:13adhere a tiny molecular compound to a gene.
30:17This compound can deactivate and sometimes activate the gene,
30:22which, however, continues.
30:24In other words, the DNA profile of the cell does not change.
30:29This could explain the differences between identical twins like Jake and Tom.
30:36Some unidentified factor present in the early stages of cellular development
30:41has caused a methyl group to be attached to the gene of Tom's chromosome
30:45related to growth.
30:47This gene continues to exist, but has been deactivated.
30:52By investigating the mystery of twins like Tom and Jake,
30:57geneticists are beginning to find clues
31:01to some of the great mysteries of the human genome.
31:19This is a map of chromosomes belonging to identical twins.
31:23On the left we have those of two three-year-olds
31:26and on the right two 50-year-olds.
31:29The areas marked in red indicate the increase in methylation
31:33that has occurred in their chromosomes over 50 years.
31:37We know that factors such as tobacco,
31:39diet and exposure to certain chemical products
31:42can interfere with the functioning of genes.
31:45The surprising thing is that differences in the environment
31:48not only occur during life, but also inside the uterus.
31:53Hormones, space, the quality of nutrients,
31:56all this can affect embryos in different ways,
32:00even those that share the same placenta.
32:03The activation and deactivation of genes
32:06during the early stages of their development
32:09could explain aspects of the fate of these twins
32:12that, however, affect us all.
32:15For example, why does a person get sick
32:18while another person is free from them?
32:21Epigenetics can also play a significant role
32:24in determining sexuality.
32:26If the sexual preference is related to an unidentified gene,
32:30it could be that the suppression or epigenetic activation of this gene
32:34dictates sexual orientation.
32:38These genetic interrupters could answer the question
32:42of why a twin absorbs more testosterone than the other,
32:45thus producing a gay twin and another heterosexual twin.
32:50It is increasingly clear that our health, personality,
32:53tastes and even our appearance
32:56are not the product of genes or the environment itself,
33:00but that nature and the environment are intimately linked,
33:04epigenetics being the biological and tangible link
33:07between these two realities.
33:10And what is most surprising is that the latest research
33:14shows that these subtle changes in the manifestation of a certain gene
33:18can be inherited by the next generation
33:21without affecting their DNA.
33:25While examining a birth and death record
33:28in a remote region of northern Sweden,
33:31some researchers discovered a curious phenomenon.
33:34A generation of children who had suffered from starvation
33:38had grandchildren who lived longer than them.
33:45On the other hand, the descendants of children
33:48who enjoyed abundant food
33:51suffered an increase in the risk of diabetes and cardiovascular diseases,
33:55as well as an increase in their mortality rate.
34:01The effect of starvation was especially marked in children
34:05who at that time were about to produce reproductive cells,
34:08that is, sperm.
34:13It seems that the genetic configuration of these reproductive cells
34:16was direct, although subtly altered
34:19by the lack or abundance of food.
34:23Through their sperm, these subjects
34:26passed on their nutritional experience to future generations.
34:30The more we explore the world of epigenetics,
34:33the more it seems that we are not a simple product of genes.
34:38We could even have the power to direct our genetic destiny
34:42and perhaps also that of our descendants
34:45through the decisions we make regarding our lifestyle,
34:48such as smoking, diet and physical exercise.
34:53What makes identical twins unique and useful for genetics
34:57is that their genomes match 100%,
35:00or at least that's what we thought.
35:04But the new techniques applied to the study of DNA
35:07tell us a different story that has only just begun.
35:16As the second trimester draws to a close,
35:19a new echography of twins will be carried out.
35:23Now we will check the development of external features
35:26such as limbs and eyes.
35:29In addition, we will examine the main organs
35:32in case there are any signs of defects.
35:35Twins are approximately 20 centimetres tall.
35:38They are so small that they fit in the palm of a hand.
35:46The echography carried out in week 20
35:49allows us to know whether the mother and her babies
35:52will be boys or girls.
35:56Gender identification can be done at 11 or 12 weeks,
36:00but it is safer at 4 months.
36:04The echography reveals that our twins are boys.
36:1224 weeks.
36:14At this time, when the twins are in their 24th week of development,
36:19their mother can feel her kicks.
36:27Inside the mother's womb,
36:30a battle for space is taking place.
36:33The echography shows this struggle
36:36and perhaps a first approach to their personalities in training.
36:41Ultrasound studies have shown that
36:45the twins' early forms of shy or extroverted behavior
36:48are combined with the observation of twins after birth.
36:57A twin study found that sometimes
37:00the shyest one grabbed his umbilical cord
37:03and even seemed to lick it,
37:06while his extroverted sister grabbed him,
37:09kicked him and pushed him.
37:12This pattern of behavior continued after birth.
37:17At the age of 4 years,
37:20the shy child showed a delayed behavior.
37:23His sister, the extroverted one,
37:26tried to grab him to play with him.
37:29It seems that our personalities begin to form in the womb.
37:43From the 29th week,
37:46the fetuses begin to look like newborn babies.
37:54Their body fat increases rapidly
37:57and their bones are fully developed,
38:00although they are still soft and flexible.
38:07The hair thickens
38:10and the fingers grow to the tip of the fingers.
38:15The fingerprints of our twins are different,
38:18which means that the epigenetic changes
38:21have already had an effect on the genes that control the fingerprints.
38:26The differences in the fingerprints will increase
38:29because as they develop, they receive blood from the veins.
38:34This causes them to swell and form different patterns.
38:38If the blood flow that comes to one of the twins
38:41from the placenta is restricted,
38:44the blood can be deflected from the fingers and other extremities,
38:47causing the fingerprints of that individual
38:50to have more lines than those of his brother.
38:53The drawing of the fingerprints can help us
38:56predict the degree of health of our heart when we are adults.
38:59More lines, more chances of heart problems.
39:08Since the moment a fertilized egg is subdivided into two,
39:11several elements of the genetic code come into action
39:14to create differences between identical twins.
39:17Distinctions that are accentuated as time goes by.
39:20However, we had always thought
39:23that identical twins had the same DNA.
39:26Until in 2007, a study was carried out
39:29by a group of researchers
39:32to study one of the strangest anomalies
39:35in the life of twins.
39:38Why does one succumb to congenital diseases
39:41and the other does not?
39:44They chose the Parkinson's disease
39:47because it is the most common disease
39:50in the life of twins.
39:53It is the most common disease
39:56in the life of twins.
40:00They chose Parkinson's
40:03because it is more likely that this disease
40:06is caused by a spontaneous genetic factor than by inheritance.
40:12The scientists examined the genes
40:15of 19 identical twin pairs,
40:18including 9 pairs in which only one of the two
40:21suffered symptoms of a genetic disorder.
40:25Their goal was to question the common perception
40:28that identical twins are also genetically identical.
40:31Their analysis revealed that there were differences
40:34in the number of genes of each twin.
40:40Normally there are two copies of each gene,
40:43one inherited from the mother and one from the father.
40:46But this study shows that it is possible to have
40:49only one copy or even three of the same gene
40:53This phenomenon, known as variation of the number of copies,
40:56can fundamentally alter the function of genes
40:59and induce some diseases in one twin and not in the other.
41:02This discovery is very important
41:05to understand both diseases and twins,
41:08as it proves that twins are not 100% genetically identical.
41:32The same definition of identical twins must be reviewed,
41:35as technological advances show that all identical twins
41:38have small but significant differences.
41:48Our identical twins are reaching the end of their uterus period.
41:53There are already small genetic differences
41:56that will configure very different lives.
42:00But before that, they must face the most dangerous phase
42:03of their uterus journey, the birth.
42:1135 weeks have passed.
42:14At this time the twins are fully developed.
42:19They have hair, eyelashes and nails.
42:25They can open and close their eyes,
42:28and their mouth.
42:31The conditions in the uterus become uncomfortable.
42:36Each of them weighs around 2 kilos,
42:39a third less than the average baby weight of a simple pregnancy.
42:50But together, the twins exert tremendous pressure on the uterus.
42:54Premature twin births before the end of the 37-week pregnancy
42:57are normal.
43:08Our twins will be born in the 35th week,
43:11through a cesarean section.
43:14More or less half of the twins are born like this,
43:17due to the difficulties and dangers of a double birth.
43:24To ensure safety,
43:27the team that will take care of the birth is bigger than normal.
43:39Quickly, the obstetric surgeon
43:42cuts the first membrane, and then the second.
43:48The cesarean sections are carried out so quickly
43:51to reduce the risk of complications.
43:58The surgeon sinks his hand into the uterus
44:01and takes out the first baby.
44:08The newborn breathes and shouts.
44:16Finally, the placenta cord is cut.
44:19His life is saved during the last 35 weeks.
44:34Acting quickly,
44:37the surgeon now looks for the second twin.
44:41With his brother out, he comes out quickly,
44:44also with his head in front.
44:49After the birth,
44:52it is not always clear
44:55whether the twins are identical or fraternal.
45:03In this case, the twins have shared the placenta,
45:06the clearest indication that they are identical.
45:10If the identical twins had different placentas,
45:13as happens sometimes,
45:16the only sure method of identifying them
45:19would have been DNA analysis.
45:30After an extraordinary journey,
45:33these two wonders of reproduction
45:36have come to the world safe and sound.
45:39Although they look the same, we know they are different.
45:47245 days ago,
45:50a fertilized egg was subdivided
45:53and created two identical embryos.
45:58From that moment on,
46:01their destinies began to take separate paths.
46:04The differences in their nutrition
46:07or in the space they occupied,
46:10a different exposure to hormones,
46:13a different epigenetic profile,
46:16even tiny differences in their underlying genome.
46:19All these factors combine
46:22to create significant differences, although subtle.
46:25Now, the twins are about to begin
46:28the next phase of their journey.
46:31As they grow,
46:34they will face different experiences and influences,
46:37so the differences between them will increase.
46:41These differences bring us closer
46:44to the answer to one of the most important questions
46:47that affect humanity.
46:50The study of identical twins
46:53has clarified the complex relationships
46:56between genetics and the environment,
46:59nature and the environment,
47:02something that makes us unique beings.
47:05Their results will have profound and lasting effects
47:08on the future of humanity.