Summary

Research into the genetic basis of homosexuality and broader sexual diversity has progressed from early 20th-century sexology to modern genomics. Von Krafft-Ebing and Hirschfeld first suggested heritable influences, and Kallmann’s twin studies in the 1950s introduced a systematic framework to separate genetic from environmental contributions to sexual orientation. Twin and related designs subsequently reported heritability estimates of 31–74% in males and 27–76% in females. Despite periodic critiques, the equal-environment assumption has remained broadly methodologically robust. Genome-wide association studies (GWAS) marked a major advance. Although early studies were limited by sample size, recent large-scale GWAS have identified significant single-nucleotide polymorphism associations with same-sex sexual behavior, reinforcing a complex, polygenic architecture. Polygenic scores (PGS) or polygenic risk scores (PRS) now offer quantitative estimates of individual genetic predisposition and may help build integrative models of human sexual behavior when combined with environmental and developmental data. Future work should harmonize phenotype definitions across identity, attraction, and behavior; aggregate measures to reduce noise; and adopt systems-level, multi-omics approaches that move beyond reductionism. Interdisciplinary collaboration across genetics, neuroscience, psychology, and social sciences is essential, in addition to greater attention to understudied domains (female homosexuality, sexual fluidity, bisexuality, pansexuality/polysexuality, asexuality, and transgender/trans-sexuality). Community-based participatory research can improve inclusivity and real-world relevance. Overall, the field has moved beyond a single gay gene toward models integrating genetic, epigenetic, and environmental influences, with sexogenomics together with GWAS, PGS/PRS and system biology providing a unifying framework that also engages ethical and societal dimensions.