Undergraduate Research Journal of Psychology at UCLA

Personality development arises from the ongoing interactions between genetic predispositions and environmental experiences throughout a person's life. This literature review synthesizes findings from published behavioral genetic studies, longitudinal twin and adoption research, molecular analyses, and environmental psychology to interpret how genetic, environmental, and gene-environment interaction processes contribute to the stability and transformation of personality traits. Evidence from twin studies and meta-analyses confirms that traits such as Extraversion, Neuroticism, and Conscientiousness are moderately to highly heritable. Regardless, this heritability remains unexplained at the molecular level, a gap known as the missing heritability problem. In contrast, nonshared environments, including unique life events and personal relationships, are shown to be more influential than shared family environments in shaping personality change, particularly during critical developmental changes. The review also explores gene-environment interactions, including how personality traits mediate stress perception and how genetic predispositions influence the selection and interpretation of environmental contexts. Despite evident advancements, the field presents limitations due to overreliance on Western populations, broad and imprecise environmental constructs, and insufficient integration of epigenetic discoveries. This review concludes that advancing a comprehensive understanding of personality requires integrative, developmentally sensitive, and culturally inclusive research that connects behavioral genetics, environmental psychology, and emerging genomic technologies.