1
Exploring the Traits of Twins
by: John Leon
from: Time Magazine, January 12, 1987
1.
Like many identical twins reared apart, Jim Lewis and Jim Springer found they have
been leading eerily similar lives. Separated four weeks after birth in 1940, the Jim
twins grew up 45 miles apart in Ohio and were reunited in 1979. Eventually they
discovered that both drove the same model blue Chevrolet, chain smoked Salems,
chewed their fingernails and owned dogs named Toy. Each had spent a good deal of
time vacationing at the same three-block strip of beach in Florida. More important,
when tested for such personality traits as flexibility, self-control, and sociability, the
twins responded almost exactly alike.
2.
The two Jims were the first of 348 pairs of twins studied at the University of
Minnesota, home of the Minnesota Center for Twin and Adoption Research. Much of
the investigation concerns the obvious question raised by siblings like Springer and
Lewis: How much of any individual’s personality is due to heredity? The center’s
answer: about half.
3.
The project, summed up in a scholarly paper that has been submitted to the Journal
of Personality and Social Psychology, is considered the most comprehensive of its
kind. The Minnesota researchers report the results of six-day tests of their subjects,
including 44 pairs of identical twins who were brought up apart. Well-being,
alienation, aggression, and the shunning of risk or danger were found to owe as
much or more to nature as to nurture. Of eleven key traits or clusters of traits
analyzed in the study, researchers estimated that a high of 61% of what they called
“social potency” (a tendency toward leadership or dominance) is inherited, while
“social closeness” (the need for intimacy, comfort, and help) was lowest, at 33%.
4.
The study finds that even a penchant for conservatism seems to have a genetic
base. One of the eleven traits, traditionalism (respect for authority, rules, standards
and high morals), was discovered to be 60% inherited. Among other traits listed at
more than 50% were vulnerability or resistance to stress, dedication to hard work and
achievement, and the capacity for being caught up in imaginative experiences.
__________________________________________________________________________
Exploring the Traits of Twins
2
5.
The director of the study, Thomas Bouchard, cautions that the numbers so far may
not be strictly accurate. “In general,” he says, “the degree of genetic influence tends
to be around 50%.” Attributing the 28-point gap between potency and closeness to
possible sampling errors, he predicted that “social potency will drop and social
closeness will creep up.”
6.
All the twins took several personality tests, answering more than 15,000 questions on
subjects ranging from personal interests and values to phobias, aesthetic judgment,
and television and reading habits. Twins reared separately also took medical exams
and intelligence tests and were queried on life history and stresses. Not all pairs
matched up as well as the two Jims. California twins Ann Blandin and Barbara
Parker, 40 showed only minor similarities. Said Blandin: “Bouchard said we were the
most different set of twins in the study.”
7.
Psychologist David Lykken, one of the Minnesota researchers, thinks the study will
shove the pendulum further away from the “radical environmentalism” of those who
believe the characters of children are more or less created by their parents and
environment. Lykken says test pilot Chuck Yeager is daring because he was
“genetically endowed with a low scale of fearlessness,” a trait that might have been
redirected or tamped down but not eradicated. Says psychologist Nancy Sega, a
member of the project: “Parents can work to make a child less fearful, but they can’t
make a child brave.”
8.
Adam Matheny of the Louisville Twin Study, the oldest of U.S. twin study groups,
says the “mechanism for change is laid down the moment a child is conceived” and
that the genes provide a “rough sketch of life.” Some psychologists who stress the
influence of
genes on behavior often speak as if nurture were a by-product of
nature.” “All of us make our own environment,” says developmental psychologist
Sandra Scarr of the University of Virginia. Lykken makes the same point: “The
environment molds your personality, but your genes determine what kind of
environment you have, seek, and attend to." Since the early 1960’s, several twin
studies have reported that identical twins reared apart are actually more alike than
those raised in the same home. Scarr thinks the reason is that parents faced with
identical twins try hard to stress differences between siblings. Says she: “Living with
the same family seems to increase intellectual similarity and decrease resemblance
in personality.”
__________________________________________________________________________
Exploring the Traits of Twins
3
9.
Some scholars, such as Princeton psychologist Leon Kamin, fear that the Minnesota
results will be used to blame the poor and downtrodden for their own condition.
Political liberals have long believed that crime and poverty are largely by-products of
destructive environments. As a result, they are usually suspicious of biological or
genetic explanations for behavior. “These are very ambiguous data that can be
interpreted any way you want to,” says Kamin. “I’m not saying that anyone is
falsifying facts or anything, just that we really know very, very little.” For the
Minnesota researchers and their allies, however, their study is just one more proof
that parenting has its limits. Says psychologist and twin researcher David Rowe of
the University of Oklahoma: “Parents should be blamed less for kids who have
problems and take credit for kids who turn out well.”
__________________________________________________________________________
Exploring the Traits of Twins