Nature versus Nurture: Human personality

Chicago-born molecular geneticist and psychologist Prof. Robert Plomin
gives a lot of backing to genes when considering the venerable debate of whether
“Nature” (genes) or “Nurture” (environment) is more important in affecting human
behavior. But the senior molecular geneticist at King’s College London largely
credits chance, or at least the environment, for his choice of profession and
his specialty.

There were 32 cousins in his immediate American family of
Polish-German origin, but he was the first among them to attend
university.

“My parents were born during the Great Depression. I went to
Catholic schools and made a little money shoveling snow from sidewalks and doing
clerical jobs because I knew how to type.” Then he received a scholarship at
DePaul University; the private Chicago institution of higher learning is today
the largest Roman Catholic university in the US.

“I did well in my high
school studies, so I received a full scholarship at DePaul. I started by
majoring in English and philosophy, but then I ended up in psychology because I
had a good adviser who encouraged me, and a lot of students moved from
philosophy to psychology.

DePaul is well known for its excellent law
school, and I thought at first about studying that, but I realized didn’t like
the idea. I was sure it was not for me.”

Then, Plomin said in an
interview with The Jerusalem Post on a recent visit to Israel during which he
delivered a lecture on “DNA and the Mind” at the Hebrew University of Jerusalem,
he received another scholarship for graduate school, this time at the University
of Texas at Austin.

“I just fell into it. I studied behavioral psychology
and took all the core courses. But as the university was the only place in the
world then that taught behavioral genetics, I took a course in that – even
though I didn’t know much about it. None of the 40 students was interested in
the subject – except me. It knocked my socks off. I hadn’t thought of behavioral
genetics; molecular genetics didn’t exist then. The animal studies seemed very
powerful.”

Thus it was luck and the people he encountered that got him
into his field, but it was certainly genetics that gave him the intelligence and
the drive to succeed and made him a leading researcher in his
field.

After receiving his doctorate in behavioral genetics from the the
psychology department at the Texas university, he went to work at the Institute
for Behavioral Genetics at the University of Colorado at Boulder where he became
professor in 1982. After a year at the Center for Advanced Study in the
Behavioral Sciences in Palo Alto, California, he moved to Pennsylvania State
University to help create an interdisciplinary research center on development
and human genetics. In 1994, he moved to England.

Plomin was at the Mount
Scopus campus of the university to participate in an International Workshop on
Temperament. Among the topics discussed were the relationship between
temperament and motivation, temperament and regulation and environmental
influences on the development of temperament.

Molecular genetics is a
field that melds biology and genetics and studies the function and structure at
a molecular level. The field studies how the genes are passed on by one
generation to the next. Molecular genetics uses the methods of genetics and
molecular biology.

An important area within molecular genetics is the use
of molecular information to study patterns of descendants and genetic mutations
that cause certain diseases, as well as why traits are carried on and how and
why some may mutate.

How physical traits are handed down from parents to
children has been well known since the Austrian monk, Gregor Mendel, formulated
the rules of modern genetics in the 19th century. Thus we know how people
inherit blue eyes, brown hair, height, fair skin and other physical
characteristics. But where human behavior comes from is still being argued. We
still don’t know how much is decided by the DNA in our cells and how much is
determined by where and how we live, our parents and siblings and various life
experiences.

Scientists have for years searched for “behavioral genes” to
explain a wide variety of behavior from violence and theft to reckless driving
and sexual orientation. Many people worry that genes could then be used to
excuse criminal behavior and get such people out of jail.

“After 40 years
of doing research on nature and nurture in psychology, there are two crucial
(not just nagging) things I want to understand,” said Plomin in his
lecture.

“One is about nature and one is about nurture. About
Nature: Behavioral genetic research has shown that genetics is important
throughout psychology. I want to find these genes in order to use them to
explore the nature/nurture interface in psychology. During the past decade,
methods have become available that can identify specific genes but it has proven
extremely difficult to find these genes; the most likely reason is that many
genes are involved and each gene has a very small effect.”

About Nurture,
he continued, “behavioral genetic research has shown that environmental
influences in psychology generally make children growing up in the same family
different, called non-shared environment. I want to know why children growing up
in the same family are so different but this has also proven
difficult.”

Plomin is Medical Research Council Professor in Behavioral
Genetics at the Institute of Psychiatry at King’s College London, where he is
deputy director of the Social, Genetic and Developmental Psychiatry Center. In
2002, he was listed “among the 20th century’s most influential psychologists” by
the Review of General Psychology.

Plomin built his reputation on
conducting numerous studies of identical (monozygotic) and fraternal (dizygotic)
twins to try to tease out behavior from genes and non-shared
environments.

If genetics didn’t play a significant part, then fraternal
twins who are usually raised under the same conditions would be alike, despite
the differences in their genes. But, while research does demonstrate that
fraternal twins do resemble each other more closely resemble than non-twin
siblings, they also show these same similarities when they are raised
separately, as in similar studies of identical twins.

“My sister – a
medical technician in Chicago – and I, who are not fraternal twins, are very
different in personality,” Plomin said in the interview. “The rules of genetics
is that ‘like begets like.’ But the second law is that non-twin siblings are not
necessarily like you, and that 50 percent of your genes are
different.

“There is a range of differences. The environment can also
make family members different.

The assumption is that family is a unit by
which environmental factors are doled out. Two kids in the same family would be
thought to be similar. But they they are probably alike in intelligence, they
can be very different in personality.”

There are turning points in life,
Plomin said.

“I had an adviser who took a personal interest in me. It
seems something like chance. I might have ended up in Chicago as a lawyer or
politician.” But he went to England, marrying a woman who works with the Medical
Research Council.

“In the last few years, advances in DNA techniques have
revolutionized behavioral genetic research. Studies on a few candidate genes
have given way to systematic genomewide association (GWA) research that scans
the entire genome for associations with complex traits.

“GWA research
shows that genetic influence on cognitive abilities and disabilities is caused
by many genes of small effect. Because the effects are so small, it will be
difficult to find and most of the genes responsible for the heritability of
cognitive traits, called the ‘missing heritability’ problem. “However, even
without identifying specific genes, it is possible to estimate genetic influence
from DNA, called ‘genome-wide complex trait analysis.’ The next big thing is
whole-genome sequencing which will capture all DNA variation throughout the
three billion base pairs of the genome.”

At King’s College, he teaches
graduate students while doing studies that have involved thousands of pairs of
twins. Some of them are adults by now, and quite a few had been raised
separately from their siblings. He and colleagues not only studied personality,
but also took DNA samples and conducted molecular genetic studies. There are not
many triplets, he added, and very large samples are needed for this kind of
research.

“If you study identical twins, you usually look for what they
have in common.

If they are fraternal twins and of the opposite sex, you
can compare them,” said Plomin. “We’ve found over the years that genetics is
much more important an influence on behavior and personality than people used to
think. It can affect everything from reading ability to the tendency for
schizophrenia.

But many laymen believe in the tabula rasa, that you can
mold children to be what you want as long as you invest time and effort in
them.”

“Tabula rasa” (blank slate) is a term coined by English
philosopher John Locke, who postulated that people acquire all or almost all
their behavioral traits from “Nurture.” But most contemporary psychologists and
anthropologists regard this position as naive and outdated.

Genetics is
also involved in musical or sports abilities.

“If children don’t have the
physique for it, which basically comes from genetics, they won’t excel. You can
improve abilities by training, but children aren’t stupid. If they see they are
not so good at something, they will leave it. My advice to parents is to expose
their children to as many experiences as they can, but they will go into what
they like and are best at.”

Plomin has also studied shyness as a trait in
children as a heritable trait. “That doesn’t mean that if you’re shy, you can’t
do anything to overcome it. But if you’re shy, you’ll likely to avoid situations
that exposes you to a lot of such encounters. Don’t regard shyness as something
that is wrong to be and that has to be fixed. I can’t understand people who love
going to cocktail parties with guest you don’t know.”

Children, he
continued, can adapt if they are shy and are dumped by their parents at a
birthday party. That’s hard. It’s better for a parent to arrange for a shy child
to go with a friend. Don’t force your child to do things that you didn’t succeed
at so you feel you have finally been good at it.”

He recalled that when
he taught genetics at Cambridge and Oxford, half of them really wanted to go
into finance instead but were urged to take genetics courses by their
families.

Plomin has also studied autism. “I’ve done surveys of parents
and teachers who accept that genetics is important in the development of autism,
but many academics aren’t clued up. Sociologists are generally unwilling to
accept the important role of genetics in autism.”

Attention-deficit
hyperactivity disorder (ADHD) is also very heritable, he said.

“There are
two components – impulsivity and intention. They are both genetically bound. You
know that such things run in families and may assume that this is evidence of
the influence of environment. But in fact, it is evidence of the workings of
genetics.”

The type of environmental influences in behavior that are most
important, he suggested, is non-shared environment, which means that they have
different experiences and teachers, have been through different things,and come
out different even though they were raised in the same place by the same
parents. Even uterine environment and parental preference for one child over the
next can affect personality. Due to non-shared environment and genetics, two
children who grow up in the same family can be just as different as those in two
different families, he said.

Obesity and overweight are influenced by how
your parents fed you and what, if any, exercise you had. But it turns out that
children in the same family generally have similar weights because of genetics.
If there are adoptive children in a family, they and the children born to the
couple do not correlate in body weight even though they were fed the same, said
Plomin.

“There is a lot of blame, especially against mothers, when a
young adult is diagnosed with schizophrenia. The mothers are accused of ‘what
they did’ to them as infants. But as it is connected to genes, you feel off the
hook.

What can you do about the genes you yourself inherited.

“So
it’s easier. Many of those who support genetic research are parents of children
with such diseases. Parents shouldn’t feel the slightest amount of guilt if they
have passed on disorders because of the genes they inherited,” Plomin insisted.

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