Human vomeronasal anatomy indexes sexual behavior and reproductive vulnerability

BACKGROUND: The biological relevance of the human vomeronasal organ (VNO) remains unresolved, and it is often considered a vestigial structure lacking sensory function. However, the VNO exhibits marked interindividual anatomical variability that may reflect underlying reproductive or neuroendocrine biology rather than chemosensory signaling. METHODS: We conducted a cross-sectional study of 102 adults (77 females, 25 males) recruited from a clinical setting between 2024 and 2025. High-resolution nasal endoscopy was used to assess VNO size, vascularity, and pit morphology, which were combined into a composite vomeronasal organ score (VNOS). Participants completed blinded, structured questionnaires assessing sexual behavior, sexual drive, and reproductive history. Associations between VNOS and outcomes were evaluated using Poisson, negative binomial, and ordinary least squares regression models adjusted for age and, where appropriate, total number of pregnancies. RESULTS: Among females, higher VNOS (range 0-18) was independently associated with a greater number of unsuccessful pregnancies after adjustment for age and total number of pregnancies, with each one-point increase corresponding to a 15% higher expected number (incidence rate ratio 1.15, 95% CI 1.09-1.22). VNOS was not significantly associated with total number of pregnancies. In the full sample, higher VNOS was associated with a greater number of lifetime sexual partners (incidence rate ratio 1.05, 95% CI 1.03-1.07) and higher self-reported sexual drive (incidence rate ratio 1.06, 95% CI 1.04-1.08). Findings were consistent across complementary modeling approaches. CONCLUSIONS: Anatomical variation of the human vomeronasal organ is associated with sexual behavior and reproductive outcomes, particularly unsuccessful pregnancies, independent of overall fecundity. These findings support interpretation of the VNO as an anatomical biomarker of reproductive biology rather than a nonfunctional remnant.