We’ve always been spellbound by nature’s clones, but in recent years twins have become much more than a curiosity. They’re a living laboratory and the key to solving the great scientific debate of our time: nature versus nurture.
Are some women destined to cheat on their husbands? Is MS hereditary? What goes on inside a teenage brain? There is no better way to solve medical mysteries and unlock the clues to human behaviour than by studying people with a common genetic blueprint.
Nature versus nurture
The “twin method” involves comparing identical twins (100 percent shared genes) to fraternal twins (50 percent).
Over the last decade, Kerry Jang, professor of psychiatry at the University of British Columbia, has collected data from nearly 1,000 pairs of Canadian twins to study mental health, post-traumatic stress and personality disorders.
Behavioural scientist Daniel Pérusse heads up the Quebec Newborn Twin Study. He and a team of doctors have been monitoring the development of twins from birth to school age, trying to decipher how big a role genes play in social adjustment.
And at the University of Western Ontario, Tony Vernon, a professor of psychology, is surveying twins to determine how heredity affects personality, including sense of humour.
More than 50 years ago, an identical twin became the world’s first successful organ donor — and recipient. When 23-year-old Ronald Herrick donated a kidney to his dying brother, Richard, it launched research that would ultimately save the lives of thousands.
No successful transplant had ever been done. But because the Herricks shared the same genes, doctors thought there would be less chance of organ rejection. After groundbreaking surgery, Richard married his Canadian recovery nurse and lived another eight years. The surgeon went on to win a Nobel Prize.
What’s the difference?
They may appear or act like carbon copies, but no two children are exactly the same. Just ask any twin’s parent.
Fraternal (dizygotic) twins come from two separate eggs, fertilized by different sperm but sharing mom’s womb.
Identical (monozygotic) twins occur when one fertilized egg divides into two. They have the same hair colour, sex and genes (but different fingerprints). Fraternal twins sometimes look eerily alike. So how to tell the difference? DNA testing is the most foolproof method; blood tests and placenta analysis are considered less reliable.
In Canada, births of twins rose 35 percent between 1974 and 1990, and triplets and other multiples climbed a whopping 250 percent. The emergence of reproductive technology is one reason for the dramatic increase. But for years, scientists have wondered why older women who aren’t on fertility drugs also conceive more twins. This year, Dutch researchers discovered the answer: Rising concentrations of follicle-stimulating hormone (FSH) that occur as women age “can cause some ovaries to go into overdrive,” leading to double ovulation.
• There are 125 million human multiples (twins, triplets, quads, etc.) on the planet.
• Ninety-five percent of multiple births are twins.
• One birth in 80 is a twin birth.
About a quarter of identical twins are “mirror” twins — meaning their features are mirror images of each other. For example, one is right-handed, the other a southpaw; one loses a tooth on one side, the other on the opposite side; one’s hair curls clockwise, the other counterclockwise. Researchers theorize that mirror image twins are the result of an egg that splits later than usual, dividing into “right-half” and “left-half” individuals.
Cryptophasia. It sounds like a horror film or a strange disease, but it’s actually the word used to describe the special language twins sometimes develop, made up of phrases only they can understand. So the next time little Samantha says “goo-goo” to twin sister Susie, she may simply be asking her to pass the pablum.
Parade of pairs
Every August, people in a small town near Cleveland think they’re seeing double. And they are.
It’s the Twins Days Festival in Twinsburg, Ohio (named Twinsburg in 1823 after Moses and Aaron Wilcox, twin settlers who married sisters, had nine children each, and eventually died within hours of each other). Last year, about 25 Canadian pairs joined the thousands who flock there for the wiener roast, the “double take” parade and the “most alike” and “least alike” contests.
But you don’t have to go south to watch a parade of pairs. In July, the Twins Weekend at the Just for Laughs comedy festival in Montreal attracts 2,500 multiples.
Famous and infamous twins
From Shakespeare’s duos to Mary-Kate and Ashley, twins make a great story. They’ve starred in legends, literature and Hollywood ever since Jacob and Esau wrestled over their biblical birthright. Twins are a classic device for mistaken identity (Twelfth Night or The Comedy of Errors), can be twice as wise (Ann Landers and Dear Abby) or seem to cause double the trouble (Jenna and Barbara Bush). Even Elvis had a twin — but his brother, Jesse, died at birth. The King once said he always felt something was “missing.”