Case studies have played a minor role in the history of personality psychology.

By Mark Leary, Ph.D., Duke University

What role, if any, does the environment play in the development of human personality?

Defining Genius and Charisma

Before delving into the role of the environment on human personality, think of someone such as Mozart. Where did that level of musical genius come from? Yes, there were some musicians in his family, but none of them came even close to his level. By the time he was five years old, Mozart was competent on the violin and keyboard, and he was already composing music. His sister was also a skilled musician at a young age, but she never showed much skill at composition.

Being a musical prodigy requires many characteristics to align just right. Many people might have part of the pattern, but it all came together for Mozart. His genius wasn’t all genetics of course. His father was a minor composer and a music teacher, and having a music teacher in the house certainly got Mozart started. If his father had been a blacksmith, and Mozart had never had an opportunity to learn music, his genius probably wouldn’t have developed. Mozart must have had some special combination of genes that his parents and siblings didn’t, even though they shared 50 percent of the same genes.

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Some researchers think that charisma is also this sort of emergenic trait. Charisma is hard to define, but we can all think of people who have a certain amount of charisma—that special magic or charm that draws people to them, seen in many entertainers.

Charisma requires many characteristics to align just right. For example, it helps if you are physically attractive; it’s hard to think of many charismatic people who are really unattractive. You also need to be at least moderately extraverted and sociable, and to have certain interpersonal skills and an ability to relate to people. Throw in some self-confidence, along with some good verbal ability.

Charisma requires many characteristics to align just right. For example, it helps if you are physically attractive, at least moderately extraverted, sociable, have certain interpersonal skills, the ability to relate to people, self-confidence, as well as some good verbal ability.

Charisma requires a combination of a high level of all of these things, each of which has some genetic basis. If you don’t have them all, you’re probably not highly charismatic. It’s possible then, for one child in a family to have the right combination of genes and exude charisma, while his brother or sister is, comparatively, introverted or less sociable.

Learn more about intelligence and genius over the lifespan

The Role of the Environment

Personality often depends on particular combinations of genes that brothers and sisters don’t necessarily share, but what about the environmental influences on personality? Consider the impact of the parents and the family environment on personality. One might expect children who are raised by the same parents in the same way in the same home ought to turn out similar, but this fact isn’t necessarily the case.

It is true that environmental influences, including parenting, affect personality. Based on genetic data, researchers have concluded that environment accounts for approximately 50 to 70 percent of personality. But researchers have also found the environments that children from the same family share with each other exert a much weaker influence on their personalities than the environments that each child experiences individually.

There are certain activities that kids in a family share—they all went together on a family vacation last year and they all had dinner with the family last night. But many experiences happen to just one child—two different second-grade teachers or one sibling plays in a band while the other does not.

Research shows that shared experiences that are common to all children in a family affect their personalities far less than unshared environmental influences that each child experiences separately. The common environments and experiences that children in a family share don’t make them as similar to each other as we might expect.

Learn more about the integration of experience in psychology

Adopted Children: Unshared Influences

One of the strongest pieces of evidence for the idea that the shared family environment does not cause children to be alike stems from research with adopted children. If the shared family environment made children similar to each other, then children with different biological parents who are adopted into the same family should have personalities that are more similar than two unrelated people who grew up in different homes. According to the latest research, they are not.

When researchers analyzed why identical twins were so similar psychologically, they found that the similarity was due almost entirely to genetics, not to the fact that they grew up in the same environment. The fact that sharing a particular environment growing up does not lead siblings to be similar surprises most people.

Shared influences are variables that are common to all children in a family—the house and town they live in, the number of TV sets and books in the house, their parents’ attitudes and values, whether the family attends church, the family’s financial situation, the relatives who visit, the family pet, family vacations, and so on.

Learn more about the development of the human brain

Unshared influences are things that children in the same family don’t share. For example, the kids probably have different sets of friends and different teachers in school. Their parents probably treat them a bit differently as well, both because each child is different, and because the parents themselves change as they have more children. The family’s finances may change when different children are different ages, and the parents’ marriage may have different ups and downs along the way so that some children may see more conflict between the parents. Brothers and sisters in the same family also have different personal experiences, different illnesses, and different injuries.

Even children growing up in the same family have many different, unshared experiences—and these differences help explain some of the variations in personality. Research has shown that unshared parts of children’s environments exert a stronger influence on personality development than the shared parts. In some studies, the shared environment exerts little or no discernible impact on personality. For example, once we control for the genetic similarity among brothers and sisters, they are barely any more similar to one another than randomly selected people—even though they grew up in the same family.

Common Questions About Environment and Human Personality

Q: Is personality genetic or environmental?

Both genetics and environment influence personality. Twin studies have found that genetics play a larger role than parental influences when it comes to behavioral outcomes, but non-shared environmental factors play an even bigger role. For instance, if one twin falls in with a bad crowd at school, that will have a huge influence on his or her behavior.

Q: What factors influence human behavior?

Many factors influence human behavior, including the environment in which one is raised, genetics, culture, and community, which includes teachers and classmates.

Q: What are two environmental influences on personality?

One environmental influence on personality is culture. For instance, some cultures dictate that children should be reserved and speak only when spoken to. Another environmental influence is school. Since children spend the majority of their time in school, this can have a huge influence on their personality. If they go to a school where violence and drug abuse proliferates, they are more likely to engage in these behaviors themselves as peer pressure can be very powerful.

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