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.