We have all heard expressions like "he has his father’s bad temper", "he is as nice as his mother", "his grandfather was also naughty as a child" and so on.

That is why, based on the fact that our way of being seems to run in the family, to what extent is personality inherited? What is more important when it comes to defining it: genes or environment? How do we know? Let’s look at it below.

Genetics and behavior, what’s the relationship?

As with most animals, we humans inherit our parents’ DNA, half of which is made up of the mother’s DNA and half of which is made up of the father’s. This genetic inheritance influences various aspects, including our behaviour, character and values . Nevertheless, and this is the point that differentiates us from animals, is that we are capable of proposing goals and having aspirations, which can be promoted by the family and cultural environment in which we live.

Another difference that sets us apart from other animals is that we humans are aware of our genetic inheritance, that is, how much we are so similar to our parents, both psychologically and physically, and, using free will, we can try to move away from what is supposed to be in our genes. This is the field of study of behavioural genetics.

Although it is known that behavioural aspects, both those that are adaptive and those that involve psychopathology, are to a greater or lesser extent inheritable, a mistaken belief before the development of the Human Genome Project was that each behaviour or aspect of personality and intelligence would be delimited by one or a reduced group of genes . However, research discovered that there was no single gene for, for example, schizophrenia, giftedness or the extraversion dimension.

Each of these aspects, and practically all human behaviour, depends on the interaction of several genes, which can be in the thousands. Each gene has a tiny impact on the personality, but together they shape it and make it similar to that of the parents.

Genes versus environment: who will win?

The influence of genes and environmental factors on an individual’s behavior is highly variable throughout life. It has been seen that families, which are themselves an environmental factor, have a major influence on a child’s cognitive abilities during early childhood. However, when these children have grown up and are old enough to go to primary school, it seems that the genes are imposed , blocking the influences of the environment.

Obviously, the claim that six-year-olds are pure heritage and no environmental influence is false. Education at school, together with contact with other children and the experience of what kind of events, benign or unfavourable, shape their way of being and their knowledge, however, it is in these years that their genetic code seems to be more relevant when it comes to determining their personality.

In fact, between the ages of three and six, children try to find an environment that suits them, that is, they select their friendships according to their way of being, they try to create an environment that is in line with their predispositions . For example, a child with a tendency to be more active is likely to be interested in sports, which will motivate him/her to practice football in the school yard and have contact with other children who enjoy this activity.

Is personality inherited?

The approach to heritability of personality has been carried out through the best type of study that behavioural geneticists could have achieved: twin studies, both with monozygotic or genetically identical twins, and with dizygotic or twin twins. These experiments are ideal, especially when identical twins have been separated at birth . Those traits that they share, despite having been raised in different homes, will be attributed to genetic factors.

Although this type of research still has some methodological problems, there are certain patterns in the results. The most powerful personality model at present is McCrae and Costa’s Big Five, in which personality is defined on the basis of five major dimensions: extraversion, friendliness, neuroticism, openness to experience and responsibility.

Studies that have studied the personality of twins, both identical and fraternal, indicate that there is a high heritability of the traits, especially being monozygotic twins. This means that if, for example, one identical twin is cordial, the other twin, with a high degree of certainty, is also cordial . This is a clear indication that personality is strongly influenced by genetic inheritance.

To what extent does genetics play a role?

When we talk about something being encoded in genes and being a product of heredity, we are talking about the concept of heritability of a certain trait. Heritability indicates what percentage of variation in the traits of two individuals is due to genetic causes . A high percentage of heritability indicates that the variation of the trait, let’s say for example being creative, has a great protagonism the genes, while a low heritability comes to say that environmental factors have a greater importance.

Research suggests that the heritability of personality traits is around 40%-50%. This means that about half of the variation in personality can be attributed to a genetic component. This should not be misunderstood, as it does not mean that half of an individual’s personality is due to genetic factors. Non-shared environmental factors would explain about 30% of the variation, and shared factors would explain 20%.

What should be clear from the concept of heritability of personality is that it does not indicate that we have about a 50% chance of inheriting our parents’ personality, or that we will share 50% of that personality. The data on heritability indicates that, for example, if one person is creative and another is less so, most of that difference is due to genetics and, to a lesser extent, it is due to having received influences from the environment, both shared and not shared.

Heritability should not be confused with the idea of genetic determination . The latter refers to the fact that genes can determine a particular trait, as long as it is known which gene or genes are involved in that determination.

Bibliographic references:

  • Vukasović, T., & Bratko, D. (2015). Heritability of personality: A meta-analysis of behavior genetic studies. Psychological Bulletin, 141(4), 769-785. https://doi.org/10.1037/bul0000017
  • Jang, K., Livesley, W.J., & Vernon, P.A. (1996). Heritability of the big five personality dimensions and their facets: a twin study. Journal of personality, 64 3, 577-91.
  • Costa, P. T., & McCrae, R. R. (1992). NEO PI-R professional manual. Odessa, FL: Psychological Assessment Resources.