Sandra and Marisa Pena, identical twins, seem to be
exactly the same. They have the same thick dark hair, the same high
cheekbones, the same habit of delicately rubbing the tip of the nose in
conversation. They had the same type of thyroid cyst at the same age (18)
in the same place (right side). When San Diego is mentioned, they both
say, simultaneously and with the same intonation, "Oh, I love San Diego!"
They live together, work one floor away from each other at MTV, wear the
same clothes, hang out with the same friends. They even have the same
dreams.
The sisters are as alike as two people can be. At the same time,
they are opposites. Sandra is outgoing and confident; Marisa is reserved.
They have the same pretty face, but those cheekbones make shy Marisa look
mysterious and brooding, while Sandra looks wholesome and sweet. Sandra
tends to speak for her sister: "Marisa's always been more quiet, more
subdued, an introvert"; Marisa nods her assent. They see themselves as a
duo—but more like complementary photo negatives rather than duplicates
of each other. "I think we balance each other out," says Sandra.
"Definitely," Marisa chimes in. Sandra begins, "In every family photo,
I'm smiling, she's"—"I'm not," Marisa says with a laugh.
When their father passed away in 1994 from pancreatic cancer
and their mother died soon after, the deeper differences between the two
became obvious. Their family had been very loving and protective, and the
sisters were traumatized by the sudden loss. But as Marisa sank into a
depression, Sandra picked up and changed her life. She left San Antonio
for Germany to live with her boyfriend. Marisa stayed put, catatonic with
sadness. It was the first time the two had ever been apart.
Then, after a few months in Germany, Sandra headed to New York
City—the buzzing metropolis in which she had dreamed of living since she
was a teenager. Marisa soon followed Sandra, but when she arrived in New
York, "She just couldn't let go of [her sadness]," says Sandra. "I didn't
know what to do with her."
We've come to believe that genes influence
character and personality more than anything else does. It's not just
about height and hair color—DNA seems to have its clutches on our very
souls. But spend a few hours with identical twins, who have exactly the
same set of genes, and you'll find that this simplistic belief crumbles
before your eyes. If DNA dictates all, how can two people with identical
genes—who are living, breathing clones of each other—be so
different?
To answer such questions, scientists have begun to think more
broadly about how genes and life experience combine to shape us. The
rigid idea that genes determine identity has been replaced with a more
flexible and complex view in which DNA and life experience conspire to
mold our personalities. We now know that certain genes make people
susceptible to traits like aggression and depression. But susceptibility
is not inevitability. Gene expression is like putty: Genes are turned on
and off, dialed up or down both by other genes and by the ups and downs
of everyday life. A seminal study last year found that the ideal breeding
ground for depression is a combination of specific genes and stressful
triggers—simply having the gene will not send most people into despair.
Such research promises to end the binary debate about nature vs.
nurture—and usher in a revolution in understanding who we are.
"While scientists have been trying to tease apart environmental
from genetic influences on diseases like cancer, this is the first study
to show this effect [for a mental disorder]," says Thomas Insel, director
of the National Institute of Mental Health. "This is really the science
of the moment."
New technological advances made it possible to
quickly identify human genes. That breakthrough launched a revolution in
human biology—and in psychiatry. Not only were scientists rapidly
discovering genes linked to illnesses such as cancer and birth defects
like dwarfism, they also found genes associated with such traits as
sexual preference and aggression as well as mental illnesses such as
schizophrenia.
Genetic discoveries transformed the intellectual zeitgeist as well,
marking a decisive shift from the idea that environment alone shapes
human personality. Nurture-heavy theories about behavior dominated in the
1960s and 1970s, a reaction in part to the legacy of Nazi eugenics. By
the 1990s, the genome was exalted as "the human blueprint," the ultimate
dictator of our attributes. Behavioral geneticists offered refreshingly
simple explanations for human identity—and for social problems. Bad
parenting, poor neighborhoods or amoral television didn't cause bad
behavior; genes did. No wonder all those welfare programs weren't
working.
"People really believed that there must be something exclusively
genetically wrong with people who are not successful. They were exhausted
with these broken-hearted liberals saying that it's all social," says
Andreas Heinz, professor of psychiatry at Humboldt and Freie University
in Berlin, who has been studying the influence of genes and environment
on behavior for years. The idea that violent behavior in particular might
be genetically "set" was so accepted that in 1992, the director of the
agency overseeing the National Institute of Mental Health compared urban
African-American youth with "hyperaggressive" and "hypersexual" monkeys
in a jungle.
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Opposites,
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photo negatives,
pretty face,
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sandra,
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