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Speaker 1: So here's your babies in four day and as we

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can see, they're identical.

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Speaker 2: Twins are as close as nature gets to human cloning.

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Their identical genetic makeup is one of the wonders of

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human reproduction. The close similarities can astound even identicals separated

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at birth often lead to strikingly similar lives with the

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same jobs, tastes, and hobbies, but identicals can also confound expectation.

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Advance in genetic science are revealing that identical twins are

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not as identical as we thought. Through state of the

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Art in the womb, four D ultrasound scans, scientifically accurate

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visual effects, and specially shot microscopy footage, we will reveal

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the hidden world of twin fetal development in a world

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where most of us are individual. Identical twins capture the imagination,

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but for scientists it's not their similarities that prove most fascinating,

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but their differences. They may not look it, but these

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boys are identical twins born with dramatically different birth weights.

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Twins like these with major physiological differences present an enormous

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opportunity to reveal truths about human identity, from fingerprints and

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intelligence to disease and even sexual orientation. Like everyone, identical

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twins begin life as a single cell a fertilized egg

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called a zygote. This cell contains twenty three pairs of chromosomes,

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tightly packed strings of genes, one set from the mother's

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egg and one from the father's sperm. Together, they make

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up the entire genetic blueprint for a new human life.

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A few hours after fertilization, the cell, with its cargo

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of chromosomes, embarks on a remarkable journey. It travels along

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the Filipian tube towards the womb. The single cell now

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starts to divide, first two, then four, then eight, each

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cell an identical replica of the other. This rapidly multiplying

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collection of cells is called a blaster, and it's here

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that nature's most remarkable reproductive anomaly can sometimes occur. Very occasionally,

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there is an event so mysterious that until recently it's

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never been witnessed. Several days after conception, the blastocyst spontaneously

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splits into two. Each new blastocyst is composed of cells

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with the same identical set of chromosomes, carrying the same

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arrangement of genes along their length. The two blastocysts now

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have the potential to develop into identical twins. Exactly how

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and why the blasticism splits is one of reeper ductive

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sciences greatest mysteries. But in two thousand and seven, during

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a laboratory study of twenty six embryos, embryologists witness this

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event for the first time. The blastocyst's outer membrane is

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called the zona pellucida, the lining inside is called the trophoblast.

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Just one cell layer thick, the trophoblast will eventually develop

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into the precenter. Within lies the inner cell mass embryonic

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stem cells that will eventually become the fetus. Over the

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course of four days, the embryologists noticed that a junction

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between a cell and the trophoblast membrane would regularly weaken,

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letting liquid leak out and causing the trothoblast to collapse

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like a balloon full of water. Then it would repair itself.

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But in two of the eggs, the embryologists spotted something

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no one had ever seen before. After the membrane collapsed,

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the inner cell mass divided in two, each clump sticking

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to a different side of the trough of blast as

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it reinflated. If these clumps were to develop in uterol,

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they would eventually grow into identical twins born from the

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same single fertilized egg. It's not surprising that most identicals

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retain a similar physical appearance as they grow up. Influence

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of genes reaches beyond how we look. Genes also affect

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personality and taste, making us flamboyant rather than shy, with

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the tape for coffee instead of tea, and a love

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of routine or desire for experimentation. Similarities between twins are

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often more than skin deep. Dennis and David Herrera of

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fifty three year old identicals from California. After high school,

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both became officers for the Los Angeles Police Department. Because

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they were raised together and went to the same school

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and had the same friends, it's impossible to say whether

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their career choice was influenced by their genes or their upbringing.

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To really test the extent to which our genes influence

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our life choices, scientists study identicals who have been separated

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at birth and raised in different environments. Daphne and Barbara

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were separated as babies and had no contact with each

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other for forty years. They were raised in very different families,

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one by a scientist, the other by a municipal gardener.

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But the similarities between them are striking and perhaps beyond coincidence.

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They both left school at fourteen. At sixteen, they both

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fell in love. In their early twenties, they each married

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their childhood sweethearts. They both suffered miscarriages at the same age,

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but went on to have children in their early twenties.

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Both have an irrational fear of blood and of falling down.

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When they met for the first time on a train platform,

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they wore almost identical clothing. The similarities are remarkable. They

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suggest that genes play a powerful role in shaping many

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aspects of our lives and personalities. But as we will see,

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it's the differences between identicals that could offer science the

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greatest opportunity, the chance to solve the age old debate

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of nature versus nurture. When these twins were born in

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two thousand and six, Jake weighed a healthy two and

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a half kilos. His twin Tom weighed just over half

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a chillo. Since they're identicals, this dramatic difference was a

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mystery for answers. Doctors look to the one environment the

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boys shared before birth. The womb. By day five, the

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two identical blastocysts have reached the womb. Now they face

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one of the most critical events in their nine month odyssey,

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one that could dramatically affect their fortunes in the womb

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and beyond. When they were born, Jake weighed two and

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a half kilos and his brother Tom half a chuilo,

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and yet they're identical, born just minutes apart. How could

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twins with the same genes look so different. The answer

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may lie not in their DNA, but in events that

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occurred in the environment they shared the womb, and the

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first most critical events is implantation. Around day six, the

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blastocyst must implant in the wall of the womb, securing

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its position for the next two hundred and fifty days growth,

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but timing is everything. Each twin will rely on a

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placenter to supply it with oxygen and nutrients, but the

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placenta only starts to develop after implantation, So blastocysts that

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split early before they implant each get their own placenter,

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but those that split late after implantation must share one.

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A shared placenter may mean one twin receives less nourishment

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than the other as a result, it grows much more slowly,

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a condition called selective intra uterine growth restriction. There are

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even rare instances when identical twins have their own presenters

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and yet developed this condition. Identicals Jake and Tom are

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one such case. Their different weights are the result of

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events that occurred long before they're born, but their effects

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may last a lifetime. In fact, the later the egg splits,

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the more critical the situation can become. This is Lakshmi,

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a three year old girl from northern India. Amazingly, only

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a few months ago, she had an additional set of

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arms and legs, and X rays revealed an extra pelvis.

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Strictly speaking, these don't belong to Lakshmi, but to her headless,

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inverted and undeveloped twin, called a parasitic twin. And yet

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the difference between a parasitic twin and a healthy twin

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is just a matter of days. In most cases, identical

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twins are created during a twelve to thirteen day window

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following fertilization. After this time, the basic embryo starts to

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organize itself into the first stages of the crude embryonic body.

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It may be that if the embryo splits during this organization,

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separation is never fully completed, and the two embryos remain fused.

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This rare reproductive accident occurs once in every two hundred

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thousand berths and usually results in conjoined twins. Identical twins

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joined at the head or body. Parasitic twins are in

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essence conjoined twins, except one twin is totally dependent on

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the other fully functional one. In Lakshmi's case, her headless

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twin relied entirely on her for survival. In November two

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thousand seven, Lakshmi underwent a delicate, twenty seven hour operation

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to remove the malformed twins, unwonted arms and legs, and

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to reconstruct her pelvis. Without this, she would most likely

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have died in her teens. The operation was a success

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and the doctor's hope she will walk unaided once implantation

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has occurred. Embryonic development is surprisingly rapid. By the end

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of the third week, a rudimentary body shape is already emerging.

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The embryo already resembles the beginnings of a body totally

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unprotected by skin and bone. On one edge, stem cells

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flow over and are assigned their fate by the organizer.

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One of the first organs to form is the heart,

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until now just a clump of muscle cells. Then, around

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day twenty two, a single cell in this dormant clump

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of muscle cells spontaneously contracts. It sets off a chain reaction,

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One after the other. Neighboring cells begin to contract until

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the entire vessel is pulsating. Two tiny hearts about the

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size of two pin heads beating together. Our twin embryos

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have approximately the same number of cells, the same DNA,

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and yet incredibly they may already be different, and those

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differences will become deeper and more profound as they develop,

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shedding light on some of the deepest mysteries of human identity.

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Is personality innate or learnt over time? Why do some

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of us succumb to disease while others remain immune? And

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from where do we get our skin color? What makes

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one person gay another straight? The answers are not as

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simple as we once thought. Remi and Kiran are fraternal twins,

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the result of two separate sperm fertilizing two separate eggs.

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The girl's parents are of mixed ancestry. This usually means

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the children will also look mixed race, but not always

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Being mixed ancestry means carrying a mixed set of genes

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for both lighter and darker skin. In Remi's case, a

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sperm with a set of genes that produce darker skinned

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children fertilized an egg with similar characteristics. In Kian's case,

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a sperm with genes that create lighter skin children fertilized

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a similar egg too. The result twins, but twins who

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look very different. Remi and Kian show us that twins

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can often confound expectation, but they are not the only ones.

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In two thousand and one, a pair of twins were

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born who at first appeared to be a boy and

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a girl. On closer inspection, it became clear that one

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had signs of both male and female genitalia. The twin

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was a hermaphrodite. Scientists believe that this happened because a

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single egg was fertilized by two sperm, one with a

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female sex chromosome and one with a male sex chromosome.

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The egg developed into a blastocyst with both male and

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female cells. The egg then divided, and each of the

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two new cells she had an extra chromosome. Resulting in

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a blastocyst composed of both male and female cells. That

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blastocyst then split to create twins. By chance. One had

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more cells with the male sex chrome and developed into

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a boy, while the other had similar numbers of cells

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with male and female sex chromosomes, resulting in a child

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with male and female genitalia. It was a startling discovery.

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Twins who are halfway between identical and fraternal, the only

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known case of semi identicals in the world. The simple

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classifications were used to are breaking down and will come

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to inform much of our newer understanding about how twins,

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and by extension, all of us develop. At five weeks,

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our identical twin embryos are beginning to take shape. Now

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curved into a C shape, their heads and tails can

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be distincts, as can hearts, spinal columns, and the beginnings

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of tiny limbuds. At this stage, the embryo looks almost

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indistinguishable to any vertebrate in the animal kingdom. These fragile creatures,

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just one and a half millimeters long, are about to

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embark on a critical period of brain development. This five

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week milestone could be another stage where identicals develop key

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differences before they're even born. Salsau and Jesus are identical twins.

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They were raised together. As they grew up, they remained

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physically similar, but their tastes and interests began to diverge.

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Celso became interested in dance and academia, while Jazeus preferred sports.

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The most surprising difference between the two brothers is that

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Celso here wearing black, is gay. The differing sexual orientation

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of identical twins is an opportunity to investigate one of

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science's most controversial questions. Are people born gay? As Celsou

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and Jazeus were raised by the same parents in the

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same household, they inevitably shared the same environment at a

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crucial time in their personal development. In the general population,

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the chance of someone being gay is less than five

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percent unless you have a gay twin. Here, the chances

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are much higher. If you're fraternal, sharing half your genes,

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there's nearly a twenty five percent chance that you will

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also be gay. If you're identical, sharing all your genes,

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there's roughly a fifty percent chance that you will also

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be gay. This suggests that there must be some genetic

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component to our sexuality. However, it can't be all down

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to genes. Otherwise all identicals would be either both gay

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or both straight. Some other factor must be at play.

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In their first few weeks, all fetuses develop along similar lines.

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If nothing changed, we would all be born. Female. Fetuses

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with the male Y chromosome will form testes at about

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week six that begin to produce the hormone testosterone, but

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at about the eighth week, testosterone is released and may

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affect early brain development. This hormone masculinizes the body. Testosterone

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also masculinizes the brain, including a part called the hypothalamus,

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part of the network which controls who we find sexually attractive.

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Some scientists believe that the more the hypothalamus is exposed

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to testosterone, the more it sets the stage for a

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sexual inclination towards women. Occasionally, a male fetus may not

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produce sufficient testosterone or its brain does not absorb enough

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to shape it along heterosexual nines. If this theory is right,

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then it may be that Celso the gay brother, absorbed

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enough testosterone to masculinize his body, but not enough to

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fully differentiate his brain. As a result, he was left

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with a desire for men. Although there are still many

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mysteries twins like these are playing a crucial role in

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informing scientists about how and when we all develop our sexuality.

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By the eighth week, our identical twins have finished their

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embryonic stage of development and are now known as fetuses

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from the Latin meaning offspring. The twins, now secure in

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their own sex but sharing a percenter, have approximately two

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hundred days left until birth. Now their growth accelerates. By

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thirteen weeks, they're beginning to look more human. The eyes

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have moved together and the head is in better proportion

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to the rest of the body. It's also the end

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of the first trimester, the time most pregnant women will

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have their initial ultrasound scan. The ultrasound sonographer checks for

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basic signs of normal development.

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Speaker 1: So here's your babies in four D. And as we

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can see the identical.

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Speaker 2: The sonographer sees a single placenta, a sure sign that

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the twins are identical.

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Speaker 1: We can see here a single percenter like a T section,

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in which proves that you're having identical twins. So when

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would you see them start interacting or reacting against each other.

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We can see them almost sort of moving.

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Speaker 2: From now on, the mother will be monitored closely twin

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pregnancies are more at risk of premature births. Immature development

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of lungs and organs can lead to complications. These complications

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make natural childbirth more dangerous. As a result, twins are

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around fifty percent more likely to be borne by cesarean

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section than Singleton's. The timing of the scan also marks

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the start of the second trimester. The second trimester, from

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twelve to twenty four weeks, will see not only dramatic growth,

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but massive development in everything from the structure of the

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brain to the refinement of facial features. By the end

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of this stage, the fetuses will be small but almost

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perfectly formed. They look very similar, but newer search reveals

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that even at this early stage, identical twins may already

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be less identical. Subtle changes are under way that will

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become greater throughout their lives, and the mechanism responsible is

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one of the most complex yet fascinating processes in the

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whole of human development. Fifteen weeks into their journey from

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conception to birth, our identical twins begin to move for

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00:29:36,720 --> 00:29:45,680
the first time. They start to interact, exploring their environment

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with their hands and feet, touching and even appearing to

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kiss their mother. In later pregnancy will feel the same case.

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Each twin feels in muteroe. At times they appear aggressive,

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at others almost caring. They look identical, but unseen influences

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00:30:15,240 --> 00:30:19,440
may already be taking effect, ones that could subtly alter

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the expression of genes in their growing body identicals. Jake

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and Tom are now aged seventeen months. Jake is eight

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centimeters taller than Tom and four kilos heavier When they

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were born in two thousand and six, doctors attributed these

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discrepancies in size and weight to restricted nutrition or blood

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flow in the womb. They expected Tom to catch up,

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but after a year and a half, they're investigating whether

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Tom may be suffering from a genetic condition called Russell's

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Silver syndrome, a growth disorder. One of the causes of

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this syndrome may be a problem with a growth gene

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on chromosome eleven. Scientists are puzzling over why Tom and

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his brother do not both have a syndrome. Identical twins,

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after all, have identical genes. Genetic puzzles like these are

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opening up a little known world at the outer reaches

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00:31:42,400 --> 00:31:51,359
of science, epigenetics. This growing field of biology may help

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00:31:51,440 --> 00:32:00,240
explain the differences between twins like Tom and Jake. Epigenetic

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00:32:00,440 --> 00:32:03,119
reveals that while their DNA code may be the same,

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00:32:04,000 --> 00:32:10,039
the way it functions can differ. The human genome contains

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00:32:10,079 --> 00:32:14,759
around twenty five thousand genes, each with its own specific function,

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00:32:15,400 --> 00:32:21,000
such as producing energy or directing cell division. Now geneticists

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00:32:21,079 --> 00:32:24,960
are investigating a previously unknown aspect of the genome called

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00:32:25,000 --> 00:32:30,160
the epigenome. There is a series of chemicals that act

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00:32:30,200 --> 00:32:37,319
as switches capable of activating or deactivating individual genes. One

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00:32:37,319 --> 00:32:41,079
of these switches works by a process called DNA methylation.

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00:32:43,279 --> 00:32:47,680
This causes enzymes insider cell to attach a minuscule molecular

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compound a methyl group, to a gene. This compound can

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deactivate or at times activate the gene, but the gene

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00:32:56,240 --> 00:33:06,400
remains the cell's DNA profile is unchaeed changed. This could

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explain the difference between identical twins Jake and Tom. Some

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as yet unidentified environmental factor in early cell development has

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caused a methyl group to attach itself to a gene

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00:33:19,160 --> 00:33:23,359
on one of Tom's chromosomes, a gene associated with growth.

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The growth gene is still there, but it's been switched off.

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By investigating the mystery of twins like Tom and Jake,

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Geneticists are finally beginning to find clues to some of

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the great mysteries of the human genome. This is a

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00:33:54,119 --> 00:33:57,720
map of chromosomes belonging to identical twins from age three

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00:33:57,759 --> 00:34:00,640
on the left to twins aged fifteen on the right.

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00:34:01,920 --> 00:34:04,960
The red markings are an indication of the increase in

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the methylation that has occurred to their chromosomes over half

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00:34:08,119 --> 00:34:12,800
a century. We know that factors like smoking, diet, and

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00:34:12,880 --> 00:34:16,800
chemical exposure can, over a lifetime, wreak havoc with how

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genes operate. What's astounding is that there are different environmental

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00:34:22,039 --> 00:34:28,079
influences in not only our lifetime, but also in utero. Hormones, space,

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00:34:28,840 --> 00:34:36,079
quality of nutrition can all affect identical embryos differently, even

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those sharing a placenta. The activation and deactivation of genes

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during early development could explain many of the twists of

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00:34:44,440 --> 00:34:48,079
fate that affect us all why one person is struck

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00:34:48,119 --> 00:34:52,840
by disease while another spared. Epigenetics may also play a

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00:34:52,880 --> 00:34:59,119
significant role in determining sexuality. If sexual preference is associated

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with an asthet unidentified gene, it may be that the

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epigenetic suppression or activation of this gene dictates sexual preference.

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00:35:12,320 --> 00:35:15,360
These genetic switches may be the answer to why one

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00:35:15,400 --> 00:35:19,400
twin absorbs more testosterone than the other, resulting in one

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being gay and the other straight. It's becoming clear that

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our health, personality, tastes, and even appearance are not the

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00:35:29,480 --> 00:35:32,800
product of either our genes or our environment, but that

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00:35:32,920 --> 00:35:38,599
nature and nurture are inextricably bound, with epigenetics the tangible

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00:35:38,639 --> 00:35:46,000
biological link between the two, and most surprisingly of all,

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new research claims these subtle changes to a gene's expression

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00:35:51,079 --> 00:35:54,800
can be passed on down through the generations without affecting

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00:35:54,800 --> 00:36:01,199
the underlying DNA. Studying a register of births and deaths

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00:36:01,559 --> 00:36:05,760
in a remote region of northern Sweden, researchers noticed a

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00:36:05,800 --> 00:36:11,400
peculiar phenomenon. A generation of boys who experienced a famine

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00:36:11,760 --> 00:36:20,679
had grandchildren who led longer lives. On the other hand,

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00:36:21,159 --> 00:36:24,400
descendants of those boys who enjoyed plentiful food as children

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00:36:25,039 --> 00:36:30,199
experienced an increased risk of diabetes, cardiovascular disease, and higher

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00:36:30,280 --> 00:36:38,320
mortality rates. The effect of famine was especially strong if

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the boy was at the age when he was just

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00:36:40,079 --> 00:36:47,119
about to start producing reproductive cells his sperm. It seems

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00:36:47,199 --> 00:36:50,960
the genetic makeup of these reproductive cells were directly but

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00:36:51,079 --> 00:36:56,960
subtly altered by the famine or feast. Through their sperm,

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they passed on a nutritional legacy to future generations. The

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00:37:03,760 --> 00:37:07,440
more we explore the hidden world of epigenetics, the more

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00:37:07,480 --> 00:37:10,559
it seems we are not simply a product of our genes.

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We may even have the power to steer our genetic

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destiny and perhaps that of our descendants, through lifestyle choices

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00:37:20,119 --> 00:37:27,360
such as smoking, diet, and exercise. What makes identicals unique

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00:37:27,440 --> 00:37:31,119
and useful to genetics is that their genome is one

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00:37:31,159 --> 00:37:38,960
hundred percent match, or at least that's what we thought. Now,

365
00:37:39,119 --> 00:37:43,880
powerful new DNA techniques are revealing a different story, one

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00:37:43,920 --> 00:37:52,000
that is only just unfolding. As the second trimester draws

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to a close, the twins will have a second scan.

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The development of external features such as limbs and eyes

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00:38:00,280 --> 00:38:03,280
will be checked, and the major organs will be examined

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00:38:03,320 --> 00:38:10,920
for signs of defects. The twins are about twenty centimeters long,

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small enough to cradle in the palm of the hand.

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The twenty week scan is the time when most mothers

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will discover whether they're having a boy or a girl.

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Gender identification can be done as early as eleven to

375
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twelve weeks, but is more certain at the four months scan.

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The scan reveals our twins are boys. Our twins are

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00:38:50,159 --> 00:38:59,760
twenty four weeks into development. Their mother can now feel

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00:38:59,760 --> 00:39:09,559
them kick inside the wound. A battle for space is raging.

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A scan reveals this struggle and perhaps even a glimpse

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00:39:14,199 --> 00:39:23,119
of emerging personalities. Ultrasound studies combined with observations of twins

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00:39:23,159 --> 00:39:28,079
after birth, show very early forms of shy or extrovert behavior.

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00:39:31,039 --> 00:39:34,800
In one study of fraternal twins, the shire twin would

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00:39:34,840 --> 00:39:38,239
occasionally hang onto his umbilical cord and even appear to

384
00:39:38,280 --> 00:39:42,800
lick it, while his sister would seek to grab, kick,

385
00:39:42,960 --> 00:39:51,320
and push him. Intriguingly, this pattern continued after birth. At

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00:39:51,320 --> 00:39:55,800
four years of age, the shy twin still exhibited retiring behavior,

387
00:39:56,679 --> 00:39:59,639
while his more extrovert sister would try to grab and

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00:39:59,679 --> 00:40:05,199
play with him. It seems our personalities may well begin

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00:40:05,280 --> 00:40:21,840
to form in the womb. From week twenty nine onwards,

390
00:40:22,239 --> 00:40:31,119
the fetuses are beginning to resemble newborn babies. Their body

391
00:40:31,159 --> 00:40:36,280
fat rapidly increases, bones are fully developed but still soft

392
00:40:36,320 --> 00:40:50,599
and pliable. Head hair grows thicker, and fingernails reach the fingertips. Already,

393
00:40:50,760 --> 00:40:57,559
our twins' fingerprints are different. Epigenetic changes have already impacted

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00:40:57,559 --> 00:41:01,400
the genes that control the pattern of the fingertips. These

395
00:41:01,400 --> 00:41:06,960
fingerprint differences will become more pronounced as the fingertips develop.

396
00:41:07,360 --> 00:41:11,239
They receive blood from the veins. This makes them swell,

397
00:41:11,920 --> 00:41:17,000
forming distinctive fingerprint patterns. If blood flow from the percenter

398
00:41:17,079 --> 00:41:20,719
in one twin is restricted, blood may be directed away

399
00:41:20,760 --> 00:41:24,679
from the fingers and other extremities, leaving this twin with

400
00:41:24,800 --> 00:41:29,440
more wells on their fingerprints than the other. Our fingerprint

401
00:41:29,480 --> 00:41:32,719
patterns can help to indicate how unhealthy our heart will

402
00:41:32,760 --> 00:41:37,440
be in adult life. The more wells, the greater the

403
00:41:37,559 --> 00:41:49,039
chance of later heart problems. From the moment a fertilized

404
00:41:49,039 --> 00:41:52,880
egg divides in two, various influences on the genetic code

405
00:41:52,920 --> 00:41:59,679
conspire to create differences between identical twins, differences that can

406
00:41:59,719 --> 00:42:05,239
become more pronounced over time. Yet it's always been assumed

407
00:42:05,559 --> 00:42:12,119
that identical twins share identical DNA until a discovery in

408
00:42:12,159 --> 00:42:19,360
two thousand and seven surprised the scientific world. Researchers set

409
00:42:19,360 --> 00:42:22,079
out to investigate one of the most puzzling anomalies in

410
00:42:22,119 --> 00:42:26,559
the life of twins, why one succumbs to a genetically

411
00:42:26,559 --> 00:42:38,039
inherited disease while the other is unaffected. They chose Parkinson's

412
00:42:38,440 --> 00:42:41,159
because it's more likely to be caused by a spontaneous

413
00:42:41,199 --> 00:42:49,639
genetic cause than be inherited. So the scientists examined the

414
00:42:49,679 --> 00:42:53,880
genes of nineteen pairs of identical twins, including nine pairs

415
00:42:53,920 --> 00:42:56,960
in which only one twin showed signs of the genetic disorder.

416
00:43:02,719 --> 00:43:06,519
They wanted to challenge the common perception that identicals are

417
00:43:06,559 --> 00:43:12,239
genetically identical. Indeed, their analysis showed that there were differences

418
00:43:12,280 --> 00:43:18,599
between the number of genes each twin had. Genes usually

419
00:43:18,599 --> 00:43:23,440
occur in two copies, one inherited from each parent, but

420
00:43:23,559 --> 00:43:26,639
this study has revealed it's possible to have just one copy,

421
00:43:27,400 --> 00:43:33,480
or to have three or more copies of the same gene.

422
00:43:33,760 --> 00:43:38,519
This phenomenon, called copy number variation, can fundamentally alter the

423
00:43:38,559 --> 00:43:42,119
genes function and may induce the disease in one twin

424
00:43:42,320 --> 00:43:58,159
and not the other. It's a major breakthrough in our

425
00:43:58,280 --> 00:44:03,639
understanding of disease and in the study of twins, because

426
00:44:03,679 --> 00:44:07,440
the discovery means that identicals are not a one hundred

427
00:44:07,480 --> 00:44:12,679
percent genetic match. The very definition of identical twins needs

428
00:44:12,719 --> 00:44:16,039
to be revised, as advances in technology can prove that

429
00:44:16,119 --> 00:44:20,039
small but significant changes are present in all identical twins.

430
00:44:24,719 --> 00:44:29,079
Our identical twin boys are approaching full urn already. There

431
00:44:29,079 --> 00:44:32,440
will be subtle genetic differences between them that may shape

432
00:44:32,639 --> 00:44:38,960
very different futures. But first they must face the most

433
00:44:39,039 --> 00:44:42,920
dangerous stage of their long journey in the womb, the birth.

434
00:44:47,840 --> 00:44:57,679
It's thirty five weeks. The twins are now fully developed.

435
00:45:01,960 --> 00:45:06,559
They have hair, eyelashes, nails, and can open and close

436
00:45:06,599 --> 00:45:14,280
their eyes and mouths. Conditions in the womb are becoming cramped,

437
00:45:15,000 --> 00:45:18,639
but around two kilos each weighs about a third less

438
00:45:18,639 --> 00:45:28,719
than the average singleton baby, but combined they put tremendous

439
00:45:28,760 --> 00:45:35,480
pressure on the womb. Premature deliveries for twins before full

440
00:45:35,599 --> 00:45:47,440
term at thirty seven weeks are common. Our twins will

441
00:45:47,480 --> 00:45:52,719
be borne at week thirty five by cesarean section. About

442
00:45:52,719 --> 00:45:55,280
half of twins are delivered this way due to the

443
00:45:55,280 --> 00:45:58,639
difficulties and dangers of giving birth to two babies naturally.

444
00:46:03,119 --> 00:46:06,480
To ensure safety, there is a larger than normal delivery

445
00:46:06,519 --> 00:46:20,159
team on hand. The obstetrician swiftly cuts the first membrane

446
00:46:20,800 --> 00:46:28,920
and then the second Caesareans are always performed quickly to

447
00:46:29,000 --> 00:46:36,199
reduce the risks of complications. He plunges his hand into

448
00:46:36,199 --> 00:46:45,199
the womb and takes the first baby out. The baby

449
00:46:45,280 --> 00:46:52,840
takes his first breath and emits a healthy screen. The

450
00:46:52,920 --> 00:46:56,480
cord to the placenta, his lifeline for the last thirty

451
00:46:56,519 --> 00:47:13,400
five weeks is finally cut. Working briskly, the surgeon looks

452
00:47:13,440 --> 00:47:19,239
for his twin. With his twin brother out of the way,

453
00:47:19,639 --> 00:47:32,760
he follows quickly, also paid first. Following birth. It's not

454
00:47:32,840 --> 00:47:36,519
always obvious to the obstetrician whether the twins are identical

455
00:47:36,719 --> 00:47:42,559
or fraternal. Our twins have a shared placenter, the clearest

456
00:47:42,599 --> 00:47:49,239
indication that they are identical. If the identicals have separate percenters,

457
00:47:49,400 --> 00:47:54,039
as happens occasionally, DNA analysis is the only sure method

458
00:47:54,039 --> 00:48:10,440
of identification. After an extraordinary journey, our two reproductive marvels

459
00:48:10,760 --> 00:48:15,159
have made it safely into the world. They may look alike,

460
00:48:15,880 --> 00:48:25,119
but we now know they are already different. Two hundred

461
00:48:25,159 --> 00:48:29,760
and forty five days ago, a fertilized egg divided, creating

462
00:48:29,840 --> 00:48:36,639
two identical embryos. From that moment onwards, their paths began

463
00:48:36,719 --> 00:48:44,800
to diverge. Inequalities in nutrition or space, differing exposure to hormones,

464
00:48:46,400 --> 00:48:52,119
small alterations in their epigenetic profiling, even minute differences in

465
00:48:52,159 --> 00:48:58,599
the underlying genome, all combined to create subtle, yet significant differences.

466
00:49:00,000 --> 00:49:04,599
Now the twins are about to embark on the next

467
00:49:04,599 --> 00:49:09,840
stage of their journey. As they grow, facing diverse experiences

468
00:49:09,840 --> 00:49:14,000
and influences, the differences between them will become ever greater.

469
00:49:18,519 --> 00:49:22,039
These differences bring us closer to answering some of humanity's

470
00:49:22,079 --> 00:49:27,400
most profound questions. The study of identical twins has shed

471
00:49:27,440 --> 00:49:30,559
new light on the complex mix of genetics and environment,

472
00:49:31,079 --> 00:49:37,239
nature and nurture that makes each of us unique. It

473
00:49:37,320 --> 00:49:41,519
has profound and far reaching implications for how we all

474
00:49:41,719 --> 00:49:42,599
lead our lives.