How does personality arise? And does it change over the course of your life?

Short answer

Personality begins to form and develop already in the womb. As soon as personality becomes measurable, it turns out to be strongly influenced by both DNA and life experiences. On average, there are certain phases in which people are more or less stable in their personality. There are also recognizable trends in how personality changes due to major life events, such as a first love or the transition from school to university or work. How someone’s personality develops varies from person to person and is therefore (you can probably guess it) very personal.

Longer answer

Personality is what makes you you: a relatively stable pattern of thinking, feeling, and behaving. Are you the life of the party or a quiet thinker? Super organized or a free spirit? Personality is often described using the ‘Big Five’ personality traits:
• Extraversion: for example, how warm, sociable, dominant, or cheerful someone is
• Neuroticism: emotional (in)stability when facing challenges or stress
• Openness: the extent to which someone seeks out new creative, adventurous, or intellectual experiences
• Conscientiousness: the degree of goal-oriented and efficient behavior, such as planning and working with attention to detail
• Agreeableness: how well someone gets along with others; being warm, empathetic, or trustworthy

In coaching and team development, the DISC model is often used to describe personality: red for Dominance (D), yellow for Influence (I), green for Stability (S), and blue for Conscientiousness (C). This method can help people gain insight into their behavior, but caution is advised when using such personality tests in recruitment processes. That’s because there is no research showing that these tests can reliably predict how well someone will perform in a job.

When does personality arise?

Personality differences are present from a very young age—even before birth. For example, you can already measure how well unborn babies, at 30 weeks, are able to ignore irrelevant sounds (a process called habituation). Babies who learn this more quickly tend to have a higher IQ later in life. Research also shows that people are consistent in how fast they habituate; a child who habituates quickly will still do so faster than others a year later. Other early-recognizable differences in personality traits include temperament (how often does a baby cry and how easily can they be soothed?) and how physically active a child is.

What determines your personality?

Like almost everything about our inner and outer selves, personality is shaped by genetic influences, environmental factors, and chance. If you don’t believe in chance, you can think of it as “everything we don’t yet understand.”

Research shows that about 50% of our personality is determined by our genes—that is, our DNA. We know this thanks to twin studies. In these studies, researchers compare identical twins (who share exactly the same DNA) with fraternal twins (who are genetically as similar as regular siblings). What they find is that identical twins tend to resemble each other much more in personality than fraternal twins. Based on these differences, researchers have been able to estimate how much influence genes have on personality.

The remaining 50% is shaped by environmental factors and chance. “Environmental factors” is a broad term. It includes things like the conditions in the womb (think hormones), upbringing, education, cultural influences, and all the experiences you have throughout your life.

How stable is someone’s personality?

Although personality is relatively stable (by definition), the degree of stability varies across age groups. Research shows that when the same people fill out personality questionnaires multiple times, the most change occurs at a young age. The older people get, the more they tend to stay the same. People’s personality is most stable around the age of 60, after which it begins to change again. However, studies also show that personality is never 100% stable. In other words, your personality can continue to change throughout your entire life.

How does personality change over a lifetime?

When we compare age groups, we see a few general trends in personality—some of which you might expect. For example, during the teenage years, people tend to become less conscientious, less extraverted, and less agreeable on average. Later, in young adulthood, this tends to balance out, and people become more emotionally stable, more conscientious, and more agreeable. Although there is less research on how personality develops in middle-aged and older adults, some studies have found that in very old age (80+), people tend to become less emotionally stable, less extraverted, less conscientious, and less agreeable.

As I mentioned earlier: what you experience in life leaves its mark on your personality. Although research on this topic isn’t always conclusive, scientists largely agree on the impact of two specific life events: (1) your first romantic relationship and (2) the transition from school to the “real world.” That first relationship often leads to greater emotional stability and increased extraversion. The transition from school to university or work is commonly associated with increased agreeableness, conscientiousness, and openness, and decreased neuroticism. Research into other major life events (such as having a child, getting married, or retiring) is less clear-cut. While these experiences can have a significant impact on personality for some people, they don’t affect everyone in the same way.

For fun: personality in animals?

As almost anyone with pets will confirm, both humans and animals have personality. What you probably didn’t know is that even individual fruit flies show stable traits that could be considered personality! For instance, some fruit flies are more active than others, prefer light or avoid it. And just like with human babies, habituation (getting used to stimuli) happens faster in some fruit flies than in others—and they behave in the same way when tested again later in life. So yes, even fruit flies have a relatively stable personality!