Final answer:
The statement in question is TRUE, as fundamental personality traits such as those outlined in the Big Five model play a significant role in shaping human behavior and psychological expression, with genetic and evolutionary factors influencing these traits. However, cultural context can also affect the expression of these traits.
Step-by-step explanation:
The statement that individual differences in fundamental personality traits account for a sizeable amount of variance in human behaviour and psychological expression is TRUE. Personality traits are relatively consistent patterns of thought and behavior, which can significantly influence how a person behaves in various situations. The Big Five, also known as the Five Factor Model, is a widely recognized model that encapsulates personality through five broad trait dimensions: conscientiousness, agreeableness, neuroticism, openness, and extraversion. Each of these traits has been shown to have genetic influencers and are stable over the lifespan.
Furthermore, from an evolutionary psychology standpoint, individual differences in personality traits can provide survival and reproductive advantages. Theories such as life-history theory and costly signaling theory suggest that traits have evolved to maximize an individual's reproductive success, indicating an underlying biological component to these traits. Additionally, trait theorists also contend that personality can be represented through certain characteristics which shape our consistent ways of behaving.
However, it is also recognized that cultural influences play a part in the expression and strength of personality traits. For example, extroversion may be expressed differently across individualistic and collectivistic cultures. Thus, while fundamental personality traits offer substantial insight into human behavior, it is important to consider the richness of cultural context as well.