Identical twins are born with identical DNA, and raised in mostly identical environments. Yet they don’t turn out exactly the same. From birth, and increasingly as they get older, twins show their individuality—both physically and in how they behave.
That’s because genetic sequences are just one of many factors that make us who we are.
For decades, scientists have studied identical twins, trying to tease apart the relative importance of genes and environment—nature and nurture.
They’ve found that genes influence a wide range of human traits, from talent and personality to disease risk. But genes never tell the whole story. Throughout our lives, genes and environment move together like partners in a dance that shapes our lives.
Ila and Sabine Minn-Murray
Live in: Berkeley
At first, even their brothers and grandmother couldn’t tell them apart. (Twins tend to be most similar at birth.) But they’re not the same. Sabine, born first, has always been a bit bigger; and she’s left-handed, while Ila is right-handed. And their mother says their voices are quite distinct.
Allison and Amanda Chan
Live in: San Francisco
Their parents and close friends can easily tell them apart, but others get confused. They’re almost always together, which might be why they tend to finish each other’s sentences. “We’ve never been separated for more than a day,” Amanda says. They agree that Amanda is more studious and more of a rule-follower, while Allison (older by one minute) is more outgoing, and more mischievous.
John and William Grady
Live in: Berkeley and San Francisco
William became the Exploratorium’s Manager of Custodial Services soon after John left that same job. Some museum staff didn’t realize he was a different person. But compare them closely, and you’ll find that William’s a bit taller and heavier than John. John is married, while William is still single. And John is more outgoing.
Brian and Anthony Pancharoen
Live in: Vallejo and Benicia
The children of Thai immigrants, Anthony and Brian are both firefighters for the San Francisco Fire Department (Anthony started six months before Brian). Growing up, their parents dressed them in different colors (Anthony, red; Brian, blue). Anthony’s half an inch taller, more outgoing, and loves to cook. Brian is quieter and more artistic. Anthony’s divorced, while Brian’s engaged.
Andrea and Amy Barish
Live in: Marin County and Oakland
Amy and Andrea weren’t certain that they were identical twins until they got a genetic test at age 40. And while acquaintances sometimes mix them up, they’re less alike than most twins. Andrea’s an inch and a half taller. She’s also had breast cancer, while her sister hasn’t. Andrea’s more adventuresome, and Amy’s more mechanically inclined.
Hannah Nunn and Helen Colcord
Live in: Napa and Portola Valley
All but inseparable as girls, Helen and Hannah wore matching clothes, answered to each other’s names, and sometimes even went on dates for each other. Then in high school their parents sent them to separate boarding schools where they began developing their own identities. Hannah studied ballet at the University of Utah, married, and moved to California, while Helen studied art at Bennington College, and moved to New York City to work in design. (They both later worked in interior design.) After some 50 years on opposite coasts, Helen recently rejoined Hannah in they Bay Area. “But I still feel like an east coast person,” she says.