Marjolaine WillemsQuentin HennocqJuan José SantanderRoman Hossein Khonsari2026-03-222026-03-22202310.1101/2023.02.20.529302https://doi.org/10.1101/2023.02.20.529302https://andeanlibrary.org/handle/123456789/84155Abstract The mechanisms determining the rotation direction and position of hair whorls are unknown. Here we report observations on twins suggesting that the morphological parameters of whorls have genetic bases, and provide comparative data on whorls from children born in the Northern and Southern hemispheres, indicating that whorl formation also depends on environmental factors. Our results underline the importance of unusual morphological phenomena for providing general information on normal developmental processes, and plead for large-scale epidemiological assessments to support our surprizing initial findings.enWhorl (mollusc)BiologyEvolutionary biologyAnatomyGeneticspreprint