Comparison of Sexual Identity in Identical Twins: A Systematic Review

Objective The aim and scope of this systematic review was to provide a comprehensive assessment of the impact nature and nurture have in influencing sexual identity, with a specific focus on the concordance or discordance of sexuality in identical twins. Design: Systematic literature review. Methods Utilizing the National University Library, Google Scholar, Credo Reference, and National Institutes of Health (NIH), twenty-three articles were collected for review. Inclusion criteria: (a) peer-reviewed texts from 1990 to 2023; (b) quantitative and qualitative studies and educational pieces categorized: Alluded to Genetics, Alluded to Environment, Nature Versus Nurture Interplay, and Human Biology, Sexuality, Behavior and History (c) written in English; descriptive details (e.g., title, data source, sample size, type of siblings, age); and core aspects (e.g., main findings, limitations, conclusion). Results Strong allusion, particularly to genetics, is made regarding the origin(s) of sexual identity. However, due to its multifaceted nature, conclusive evidence has not been established. Even identical twins raised in the same environment may develop different sexual identities due to individual differences (e.g,, IQ, reactions, social circles, hobbies, preferences, and beliefs). Conclusion Further exploratory research, quantitative analysis, methodological improvements, and integrated collaboration will provide knowledge to facilitate more impactful interventions, destigmatization initiatives, and policy development aimed at fostering equality and well-being for individuals of all identities (e.g., educational programs and training, human rights advocacy, community outreach, funding allocations, and support services).