Identical Twins: Not As Similar As We Think... National Geographic Channel Takes You In The Womb To Reveal The Hidden World Of Twin Fetal Development

Using State-of-the-Art 4-D Ultrasound, See the Remarkable Developmental Differences in Identical Twins

In the Womb: Identical Twins premieres Sunday, December 21 at 9:00 p.m. ET/PT

Identical twins are as close as nature gets to human cloning.  They look alike, sound alike and can often lead strikingly similar lives - with the same jobs, tastes, hobbies, love interests and phobias.  But "clones" they are not, as any parent will attest.  Now, with state-of-the-art 4-D ultrasound, National Geographic Channel goes In The Womb to reveal the hidden - and surprisingly different - world of twin fetal development.

The fourth installment of NGC's critically acclaimed series In The Womb: Identical Twins, premiering Sunday, December 21 at 9:00 p.m. ET/PT, explores the mysterious world of twin fetal development, shedding new light on the discovery that identical twins are more different than first thought.  Through 4-D ultrasound technology, scientifically accurate visual effects and specially shot HD microscopic footage, NGC provides a revealing look at the latest findings in fetal development and genetics, including the fact that identical twins aren't a 100 percent genetic match.  Then we examine a puzzle: identical twins who share the same set of genes, yet look very different.

Witness the moment when a single cell rapidly multiplies into a blastocyst. It's here that nature's most remarkable reproductive anomaly can sometimes occur, when the blastocyst spontaneously splits into two.  Exactly how and why it splits is one of reproductive science's greatest mysteries.  Go In The Womb: Identical Twins to observe the miraculous event, first seen by embryologists in 2007, and stay in-utero to behold many milestones between fertilization and the birth of identical twins.

Born from the same single fertilized egg, it's not surprising that most identicals retain a similar physical appearance as they grow up . . . but the influences of genes reach beyond our physical looks.  In The Womb: Identical Twins traces the lives of twins of all shapes and sizes to illustrate how genes also affect personalities, sexual preferences and other characteristics.

To test how genes influence life choices and attempt to solve the age-old debate of nature versus nurture, scientists study identicals separated at birth and raised in different environments.  Meet Daphne and Barbara. Separated as babies, they had no contact with each other for 40 years.  They were raised in very different families - one by a scientist, the other by a gardener.  The similarities between them, however, are striking: both left school at 14; both married in their early 20s to childhood sweethearts; both suffered miscarriages at the same age; and both have an irrational fear of blood; they even wore nearly identical clothing when they met each other for the first time.

Their similarities are remarkable and typical of what we already know about identical twins, but as In The Womb: Identical Twins reveals, it's the differences between them that offer science the greatest opportunity.

Next, it's a genetic puzzle: identical twins who share the same set of genes, yet look very different.  When Jake and Tom were born in 2006, Jake weighed a healthy 6 pounds, but his "identical" twin Tom weighed just over one pound.  Doctors initially attributed this discrepancy to restricted nutrition and blood flow in the womb, but researchers soon realized this was not the case.  Using real-time, moving 4-D ultrasound imagery, scientists go inside the womb to examine how blastocysts develop differently and how one identical twin can physically differ so greatly from the other.

In The Womb: Identical Twins investigates differences that spring from epigenetics, the unexpected activation or deactivation of genes  These changes may help explain differences between identical twins - such as why one person is struck by disease while another is spared - and reveals that while their DNA code may be the same, the way it actually functions can differ.

Epigenetics may also play a significant role in determining sexuality and why one identical twin can be born homosexual and the other born heterosexual.  Identical twins Celso and Jesus were raised by the same parents in the same household, yet only Celso is gay.  The different sexual orientation of identicals is an opportunity to investigate one of science's most controversial questions: are people born gay?  NGC looks to their fetal development to help answer this question.

From the moment the fertilized egg divides and creates two identical embryos, In The Womb: Identical Twins examines the minute differences of their 245-day development journey: from inequalities in nutrition or space to differing exposure to hormones to small alterations in their epigenetic profile, all of which combine to create subtle yet significant differences.  As they grow and encounter diverse experiences and influences, the differences between them will become ever greater.

But these differences will also bring us closer to understanding heredity, personality, development and disease - and may profoundly impact our understanding of what makes each of us unique.

In the Womb: Identical Twins is produced for the National Geographic Channel by Pioneer Productions. For Pioneer Productions, executive producer is Simon Andreae and Andrea Florence and director/writer is Lorne Townend.  For the National Geographic Channel, executive producer is Jenny Apostol, senior vice president of special programming is Michael Cascio and executive vice president of content is Steve Burns.