Personality traits have been linked to genes, and they are constant throughout life, as judged through various personality tests that are self-taken or assessed by other people.
This is one of the simplifed views of personality traits, or OCEAN
The Big Five personality traits can be summarized as follows

From Wikipedia)
Openness to experience - Appreciation for art, emotion, adventure, unusual ideas; imagination and curiosity (vs conservatism).
Conscientiousness - A tendency to show self-discipline, act dutifully, and aim for achievement (spontaneousness vs planned behaviour).
Extraversion - Energy, surgency, and the tendency to seek stimulation and the company of others.
Agreeableness - A tendency to be compassionate and cooperative rather than suspicious and antagonistic towards others (individualism vs cooperative solutions).
Neuroticism - A tendency to easily experience unpleasant emotions such as anger, anxiety, depression, or vulnerability (emotional stability to stimuli).
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