Final answer:
The statement that personality is largely established by age 20 and remains stable is true. The Big Five personality factors show general consistency over a lifespan, with some variability due to life experiences. Personality is shaped by genetic predispositions and environmental factors such as culture and familial relationships.
Step-by-step explanation:
The statement that basic personality is established quite early in life, perhaps by the age of 20, and is relatively stable throughout adulthood is largely considered to be true. Research in personality psychology suggests that while personality can be somewhat malleable in childhood and adolescence, by early adulthood, our personalities tend to stabilize. Factors such as temperament are thought to have a biological basis and can manifest early in life. Nevertheless, environmental factors such as culture and familial interactions can influence personality expression.
Studies of the Big Five personality factors, including conscientiousness, agreeableness, neuroticism, extroversion, and openness, indicate that these traits are fairly consistent over time. However, there might be slight increases or decreases in some traits; for example, conscientiousness and agreeableness tend to increase with age, while neuroticism and extroversion might decline slightly. These traits have been found to be universal across various ethnicities, cultures, and ages, and they have considerable biological and genetic components.
In early adulthood, people also focus on developing intimate relationships and a sense of self, which are crucial for the social aspects of personality. Therefore, although much of our personality is established by early adulthood, life experiences and environmental factors continue to influence its development throughout our lifespan.