Have you ever thought about the inheritance of personality?
Is our personality something we’re born with, or is it determined by the environment we grow up in?
In fact, it has become clear that both genetics and environment are involved in individual differences in personality.
Recently, a meta-analysis study conducted through collaboration of researchers worldwide showed that the heritability of personality is approximately 40% on average.
In other words, 40% of individual differences in personality can be explained by genetic factors, while the remaining 60% is due to environmental influences.
Also, while average personality differs between men and women, there appears to be no significant gender difference in the heritability of personality.
However, it has been suggested that the patterns of genetic and environmental influences may differ slightly between men and women.
So, do research results from overseas and Japan match? Do the influences of genetics and environment differ by culture and country?
Let’s explore how our personality is shaped through studies of twins and adoptees.
Once again, personality researcher and author of Villain Encyclopedia, Tokiwa (@etokiwa999), will provide the explanation.
※We have developed the HEXACO-JP Personality Assessment! It has more scientific basis than MBTI. Tap below for details.
目次
The Influence of Genetics and Environment on Personality
What Determines Individual Differences in Personality?
Individual differences are formed through the influence of both genetics and environment.
In other words, our personality is determined by a combination of innate factors and environmental factors in which we were raised.
For example, the following factors are thought to influence individual differences in personality.
- Genetic factors: personality traits inherited from parents
- Family environment: parental attitudes and family atmosphere
- Social environment: school, peer relationships, cultural background
These factors interact in complex ways to form each person’s unique personality.
It has also been found that the influence of genetics and environment varies by personality trait.
For example, some research results show that extraversion is relatively strongly influenced by genetics, while agreeableness is strongly influenced by environment.
Thus, individual differences in personality are created through the interaction of genetics and environment. Our personality is an expression of individuality woven by our innate qualities and the environment in which we were raised.
Twin Studies Investigating the Influence of Genetics and Environment
Twin studies are a representative method for investigating the influence of genetics and environment on personality.
Twin studies compare the personality similarities between monozygotic (identical) twins and dizygotic (fraternal) twins.
- Monozygotic twins: twins from the same fertilized egg, genetically identical
- Dizygotic twins: twins from different fertilized eggs, sharing 50% of their genes
If monozygotic twins show greater personality similarity than dizygotic twins, that personality trait is considered to be strongly influenced by genetics.
Additionally, by comparing the personalities of twins raised in separate environments, we can examine the influence of environment in detail.
Thus, twin studies are a powerful method for analyzing the influence of genetics and environment on personality.
Through twin studies, we can understand the mechanisms by which individual differences in personality arise.
Personality Heritability is Approximately 40% on Average
According to meta-analyses that collected and analyzed twin studies from around the world, personality heritability is approximately 40% on average.
Heritability refers to the proportion of individual differences in personality within a population that can be explained by genetic differences. For those who find this difficult to understand, please see below.
In other words, 40% of individual differences in our personality are due to innate genetic factors, while the remaining 60% are due to environmental factors.
However, this heritability varies by personality trait.
For example, the following research results have been reported.
- Heritability of extraversion: 40-60%
- Heritability of neuroticism: 40-50%
- Heritability of openness: 40-60%
Thus, the influence of genetics varies by personality trait.
Additionally, heritability changes depending on the environmental conditions of the population. In other words, personality heritability may differ in different cultures and societies.
The finding that personality heritability is approximately 40% indicates that our personality is determined by both innate factors and environmental factors.
The expression of individuality woven by genetics and environment is our personality.
Genetic Research on Japanese Personality
Results of Twin Studies Targeting Japanese People
A representative study is the research conducted by Juko Ando and colleagues.
In this study, the following heritability rates for personality traits were reported. The remainder is non-shared environment, with no shared environment.
- Neuroticism: approximately 45%
- Extraversion: approximately 45%
- Openness: approximately 52%
- Agreeableness: approximately 35%
- Conscientiousness: approximately 52%
Let me explain in more detail.
Openness Has a Large Genetic Influence
Openness is influenced by genetics for more than half.
It is a trait of being interested in new experiences and ideas. The heritability of this personality trait is reported to be approximately 52%.
- Curiosity to try new things
- Interest in arts and creativity
- Flexibility of thinking
Furthermore, people with high openness can think about things from various perspectives.
They are also more accepting of different cultures and opinions. As a genetic factor, it is believed to be related to the active functioning of specific brain regions.
On the other hand, environmental factors cannot be ignored. Education and travel experiences are also factors that enhance openness.
In summary, openness is influenced by both genetics and environment, but genetic influence is particularly large. Therefore, this trait can be said to be partially genetically determined.
Agreeableness Has Greater Environmental Influence Compared to Other Traits
Agreeableness is a personality trait that is particularly strongly influenced by the environment.
This trait refers to emphasizing harmony with others and valuing empathy and cooperation. The heritability of this personality trait is relatively low at approximately 35%.
- Consideration and understanding for others
- Cooperativeness within groups
- Valuing harmony in interpersonal relationships
Such traits are largely shaped by family environment and school education. For example, guidance that encourages cooperation from parents and teachers can have an influence.
Furthermore, friendships and social activities are also factors that nurture agreeableness. These environments play a role in enhancing an individual’s interpersonal relationship skills.
Ultimately, agreeableness is a personality trait that is greatly influenced by environment. Therefore, the surrounding environment and education play an important role in forming this personality.
Twin studies targeting Japanese people have shown that personality traits such as conscientiousness and diligence are relatively strongly influenced by shared environment.
In the research by Juko Ando and colleagues, the heritability of conscientiousness was estimated to be approximately 20-30%.
This means that the majority of individual differences in conscientiousness are explained by environmental factors, particularly the influence of shared environment.
Conscientiousness is a personality trait with the following characteristics.
- Diligence: Being persistent and making steady efforts
- Discipline: Following rules and being punctual
- Cautiousness: Thinking carefully before acting
These characteristics are thought to be strongly influenced by environmental factors such as education at home and school, and social norms and values.
Genetically, the following factors appear to be involved.
- Impulse control: The ability to suppress desires and work toward goals
- Stress tolerance: The power to overcome stress and work persistently
In this way, conscientiousness is formed under the influence of both environmental and genetic factors.
It has become clear that conscientiousness and diligence in Japanese people are strongly influenced by shared environment.
To nurture these personality traits, education and experiences in families, schools, and society are considered to play important roles.
Genetic Research on Danish Personality
Danish Twin Genetic Research
In this country, the influences of genetics and environment on personality are being studied using nationwide data.
This is one of the world’s largest registries collecting data on Danish twins from the 1870s to the present.
Research using this registry analyzed the genetic and environmental influences on personality through the following procedures:
- Conducted NEO-FFI personality tests on twins
- Compared personality similarities between identical and fraternal twins
- Estimated genetic and environmental influences using structural equation modeling
Research using the Danish twin registry showed moderate heritability for each dimension of the Big Five.
Specifically, the following heritability rates have been reported:
| For Women | Genetics | Shared Environment | Non-shared Environment |
| Openness | 41.9% | 9.7% | 48.4% |
| Conscientiousness | 25.6% | 13.3% | 61.2% |
| Extraversion | 30.7% | 24.6% | 44.8% |
| Agreeableness | 30.9% | 0% | 69.1% |
| Neuroticism | 14.4% | 26.0% | 59.6% |
| For Men | Genetics | Shared Environment | Non-shared Environment |
| Openness | 49.0% | 0% | 51.0% |
| Conscientiousness | 45.2% | 0% | 54.9% |
| Extraversion | 50.0% | 0% | 50.0% |
| Agreeableness | 15.4% | 26.6% | 58.1% |
| Neuroticism | 55.8% | 0% | 44.2% |
Let’s now look at more specific results for each dimension.
Extraversion Heritability is 30-50%
The heritability of extraversion is reported to be around 30-50% depending on the study.
To describe this trait in one word, it represents personality characteristics such as being sociable, active, and assertive.
The Danish twin study showed the following heritability rates for extraversion:
- Women’s extraversion heritability: 30.7%
- Men’s extraversion heritability: 50.0%
Genetic factors appear to play a relatively large role in individual differences in extraversion.
However, there are gender differences in extraversion heritability, suggesting that men may be more influenced by genetics than women.
Environmental factors are also involved in the expression of extraversion.
- Family environment: Parental attitudes and family atmosphere
- Social environment: School, workplace, friendships, etc.
Thus, extraversion is formed through the influence of both genetics and environment.
While the heritability of extraversion is estimated to be around 30-50%, it may vary depending on gender, culture, and social environment.
Agreeableness Heritability is 15-30%
The heritability of agreeableness is reported to be around 15-30% depending on the study.
To describe this trait in one word, it represents personality characteristics such as compassion for others, cooperative attitude, and altruism.
The Danish twin study showed the following heritability rates for agreeableness:
- Women’s agreeableness heritability: 30.9%
- Men’s agreeableness heritability: 15.4%
Environmental factors appear to play a relatively large role in individual differences in agreeableness.
In particular, the following environmental factors are thought to influence the development of agreeableness:
- Family environment: Parenting attitudes and family relationships
- Social environment: Interpersonal relationships at school and in the community
- Cultural background: Cultural values of collectivism vs individualism
In this way, agreeableness is formed under strong environmental influence.
However, there are gender differences in the heritability of agreeableness, with research suggesting that women may be more susceptible to genetic influence than men.
The heritability of agreeableness is estimated to be around 15-30%, but it may vary greatly depending on gender, culture, social environment, and other factors.
Heritability of conscientiousness is 25-45%
The heritability of conscientiousness is reported to be around 25-45% according to research.
In a word, this trait represents personality characteristics such as being diligent, disciplined, and reliable.
A Danish twin study showed the following heritability of conscientiousness.
- Female conscientiousness heritability: 25.6%
- Male conscientiousness heritability: 45.2%
Individual differences in conscientiousness appear to involve both genetics and environment.
In particular, the following environmental factors are thought to influence the development of conscientiousness.
- Family environment: Parenting attitudes and educational policies
- School environment: Academic achievement and relationships with teachers
- Social norms: Sense of norms in culture and society
In this way, conscientiousness is formed through the interaction of genetics and environment.
Furthermore, there are gender differences in the heritability of conscientiousness, with research suggesting that men may be more susceptible to genetic influence than women.
The heritability of conscientiousness is estimated to be around 25-45%, but it may vary depending on gender, culture, social environment, and other factors.
Heritability of openness is 41-49%
The heritability of openness is reported to be around 41-49% according to research.
In a word, this trait represents personality characteristics such as having strong intellectual curiosity and being open to new experiences.
A Danish twin study showed the following heritability of openness.
- Female openness heritability: 41.9%
- Male openness heritability: 49.0%
Genetic factors appear to play a relatively large role in individual differences in openness.
However, environmental factors are also involved in the expression of openness.
- Educational environment: Abundance of learning opportunities and educational policies
- Cultural background: Whether the culture values creativity and uniqueness or not
- Socioeconomic status: Educational level, occupation, income, etc.
In this way, openness is formed under the influence of both genetics and environment.
Furthermore, there are gender differences in the heritability of openness, with research suggesting that men may be more susceptible to genetic influence than women.
The heritability of openness is estimated to be around 41-49%, but it may vary depending on educational environment, culture, socioeconomic status, and other factors.
Heritability of neuroticism is 14-56%
The heritability of neuroticism is reported to be around 14-56% according to research.
In a word, this trait represents personality characteristics such as anxiety, depression, and emotional instability.
A Danish twin study showed the following heritability of neuroticism.
- Female neuroticism heritability: 14.4%
- Male neuroticism heritability: 55.8%
Individual differences in neuroticism appear to involve a complex interaction of both genetic and environmental factors.
In particular, the following environmental factors are thought to influence the expression of neurotic tendencies.
- Stressful living environments: Excessive stress and psychological pressure
- Interpersonal relationships: Interpersonal conflicts and lack of support
- Traumatic experiences: Psychological trauma such as abuse, accidents, and disasters
In this way, neurotic tendencies are formed through the interaction of genetic predisposition and environmental factors.
Additionally, there are significant gender differences in the heritability of neurotic tendencies, with evidence suggesting that men may be more susceptible to genetic influences than women.
The heritability of neurotic tendencies is estimated to range broadly from 14% to 56%, but may vary greatly depending on gender, stressful environments, culture, and other factors.
Gender Differences in Personality Heritability
Average personality values differ between men and women
In other words, men and women differ on average in the strength of certain personality traits.
A Danish twin study reported the following gender differences in personality traits.
- Traits higher in women: Agreeableness
- Traits higher in men: Extraversion, Conscientiousness, Neuroticism, Openness
However, it should be noted that these gender differences are differences in average values, and individual differences are large.
Gender differences in personality may be created by the following factors.
- Biological factors: Differences in hormones and brain structure/function
- Social factors: Differences in gender roles and social expectations
- Cultural factors: Cultural differences in male and female roles and values
Thus, gender differences in personality are created through a complex interplay of biological and sociocultural factors.
It should be noted that gender differences are generally small, with individual differences being larger.
This is thought to be created through complex interactions between biological and sociocultural factors.
The influences of genetic and environmental factors on personality show different patterns between men and women
The influences of genetic and environmental factors on personality can show different patterns between men and women.
In other words, the relative importance of genetic and environmental factors for individual differences in certain personality traits may differ between men and women.
The Danish twin study reported the following gender differences in the influences of genetic and environmental factors on personality.
- Significant shared environmental influence only in women: Extraversion, Conscientiousness, Neuroticism, Openness
- Significant shared environmental influence only in men: Agreeableness
*Shared environment: While not strictly accurate, please think of shared environment as “family environment” for now.
In other words, for individual differences in extraversion, conscientiousness, neuroticism, and openness, shared environment appears to play an important role in women, while genetic influences are greater in men.
On the other hand, for individual differences in agreeableness, shared environment appears to play an important role in men, while genetic influences are greater in women.
Thus, patterns in the influences of genetic and environmental factors on personality show differences based on gender.
However, why these gender differences occur is still not clear.
In this way, patterns in the influences of genetic and environmental factors on personality can show gender differences. Further research is needed regarding the causes.
The Complex Relationship Between Personality Genetics and Environment
Personality heritability differs by trait
When averaged overall, it has been shown to be approximately 40%.
In other words, 40% of individual differences in personality are explained by genetic factors, while the remaining 60% are explained by environmental factors.
However, this heritability has been shown to differ greatly depending on the personality trait.
Additionally, even for the same personality trait, as seen in comparisons between Japan and Denmark, it can be understood that heritability estimates vary by country and region.
The following factors may be considered as background to this.
- Differences in measurement scales: Heritability estimates may differ depending on the method of measuring personality traits
- Sample characteristics: Heritability may differ in samples with different ages or cultural backgrounds
- Influence of environmental factors: Heritability can change depending on the magnitude of environmental factor influences
Therefore, it should be noted that personality heritability merely represents average tendencies, with large individual and situational differences.
Nevertheless, the finding that approximately 40% of individual differences in personality are explained by genetic factors provides important insights for understanding personality.
While personality heritability averages around 40%, it has been shown to differ greatly depending on the trait.
The influences of personality genetics and environment also differ by culture and country
The influences of genetic and environmental factors on personality may also differ by culture and country.
This time, we introduced meta-analyses of many studies and the influence of genetics and environment on personality in Denmark and Japan.
However, it is not yet clear whether these findings also apply to other cultural regions and countries.
This is because the following factors may differ depending on culture and country.
- Genetic background: Genetic diversity differs by race and ethnicity
- Influence of environmental factors: Educational systems, social systems, values, etc. differ
- Meaning of personality traits: How personality traits are perceived and valued differs
For example, collectivistic and individualistic cultures would value different personalities.
Thus, considering cultural context is important for understanding the influence of genetics and environment on personality.
However, there is not yet sufficient research accumulated on these possibilities.
Further cross-cultural comparative research is needed to clarify whether the influence of genetics and environment on personality differs by culture and country.
It is important to consider the interaction between genetics and environment to understand individual differences in personality
It is important to consider the interaction between genetics and environment to understand individual differences in personality.
Research to date has revealed that both genetic and environmental factors are involved in individual differences in personality.
However, genetics and environment do not exert their influence independently.
Rather, genetics and environment interact in complex ways to create individual differences in personality.
For example, the following interactions are conceivable.
- Gene-environment correlation: People with certain genetic predispositions tend to seek certain environments
- Gene-environment interaction: The influence of environmental factors varies depending on genetic predisposition
In other words, even when placed in the same environment, if genetic predispositions differ, the manifestation of personality traits will differ.
Also, even with the same genetic predisposition, if the environment differs, the manifestation of personality traits will differ.
Such gene-environment interactions are gradually being revealed through twin studies and molecular genetics research.
However, many aspects remain unexplored.
To understand individual differences in personality, it is important to focus on the interaction between genetics and environment rather than considering their influences separately.
This requires integrating knowledge from various fields such as psychology, genetics, and social sciences.
Conclusion
We have explored the complex relationship between genetics and environment regarding how individual differences in personality arise.
It has become clear that the influence of genetics and environment differs depending on aspects of personality such as extraversion and agreeableness.
Also, research from Japan and Denmark suggests the possibility that the influence of genetics and environment on personality may differ by culture and country.
However, our personality is not influenced by genetics and environment separately.
Through gene-environment correlations and interactions, both factors intertwine in complex ways to create each person’s individuality.
That is precisely why focusing on gene-environment interactions is important for understanding individual differences in personality.
Personality is an expression of irreplaceable individuality woven from innate traits and the environment in which one was raised.
By exploring the complex relationship between genetics and environment, we may gain clues to understanding each of our unique individualities.
Writer & Supervisor: Eisuke Tokiwa
Personality Psychology Researcher / CEO, SUNBLAZE Inc.
As a child he experienced poverty, domestic abuse, bullying, truancy and dropping out of school — first-hand exposure to a range of social problems. He spent 10 years researching these issues and published Encyclopedia of Villains through Jiyukokuminsha. Since then he has independently researched the determinants of social problems and antisocial behavior (work, education, health, personality, genetics, region, etc.) and has published 2 peer-reviewed journal articles (Frontiers in Psychology, IEEE Access). His goal is to predict the occurrence of social problems. Spiky profile (WAIS-IV).
Expertise: Personality Psychology / Big Five / HEXACO / MBTI / Prediction of Social Problems
Researcher profiles: ORCID / Google Scholar / ResearchGate
Social & Books: X (@etokiwa999) / note / Amazon Author Page