Enamel nanocrystal misorientation increased with meat-eating and agriculture

Article Enamel nanocrystal misorientation increased with meat-eating and agriculture https://doi.org/10.1038/s41586-026-10583-8 Received: 11 June 2025 Accepted: 22 April 2026 Pupa U. P. A. Gilbert1,2,3 ✉, Daniel R. Green4, Patrick Mahoney5, Debbie Guatelli-Steinberg6, W. Scott McGraw6, Emma Lagan6, Fredrick Kyalo Manthi7, Samuel Muteti7, Emmanuel Ndiema7, Fernando Ramirez Rozzi8,9, Cayla A. Stifler1, Connor A. Schmidt1, Barat Q. Achinuq10, Andreas Scholl10, Benjamin Gilbert11,12 & Mackie C. O’Hara13,14 ✉ Published online: 3 June 2026 Open access Check for updates Enamel covers teeth, is the hardest tissue in the vertebrate body and has a complex multiscale structure from nanometres to millimetres1. The structure comprises thin, long hydroxyapatite (Ca5(PO4)3OH) nanocrystals2, 50–70 nm wide, many micrometres long, parallel and bundled into approximately 5-µm-wide rods. The rods undulate and cross into a microscale ‘decussation pattern’ that toughens enamel by deflecting cracks3,4. However, the crystallographic orientation of enamel nanocrystals is poorly understood. Here we show that the misorientation angle of adjacent nanocrystals varies markedly across 12 primate teeth spanning 9 species, 17.8 million years of evolution and diverse diets. Using a method called Polarization Enabled Large Input of Crystal Angles at the Nanoscale (PELICAN)5, we compare nanocrystals in the same (pre)molar locations and show that misorientation increases with food hardness in extant and fossil non-human apes and monkeys. We compare misorientation across three major dietary shifts in human evolution: the transition to meat-eating about 2.0–1.5 million years before present6,7, to agriculture (about 12,000 years before present)8,9, and the Industrial Revolution (about 250 years before present)10. We show that over the past 1.6 million years, in the human lineage misorientation increased with time, especially when meat and stone-ground grains were introduced into human diets, but not with the Industrial Revolution. Thus, besides macro-changes, teeth adapted to dietary change at the nanoscale and crystallographically. This observation suggests that misorientation may contribute to enamel’s resilience; thus, bioinspired materials may consider small misorientation angles for added resilience. Enamel-like tooth structure is common to nearly all vertebrates and has been evolving since it first appeared in conodonts nearly 400 million years before present (bp)11. Enamel varies and evolves at multiple structural levels and developmental stages. The structure and properties of enamel differ at different scales. At the macroscale, the thickness and shape of enamel can evolve quickly in response to the mechanical properties of food12,13. For example, teeth that have thick enamel14 and blunt cusps are adapted to hard and abrasive foods, whereas teeth with thin enamel wear obliquely and have shearing edges suited for slicing soft foods13,15. Hard-food consumption is associated with several dental adaptations in modern primates that resist crack propagation, including large teeth, low-crowned molars and premolars, and thick, unevenly distributed enamel13,16,17. Thick enamel at the millimetre scale helps prevent crack nucleation18. At the micro- and nanoscales, enamel structure evolved to limit crack widening and propagation, thereby improving fracture resistance, also known as fracture toughness, or simply toughness3,19. At the microscale, decussating enamel prevents cracks from widening and propagating by deflecting them20 at the interface between rod and interrod enamel21. At the nanoscale, researchers originally incorrectly assumed that adjacent nanocrystals within rods are co-oriented because they elongate parallel to one another morphologically, but they actually vary in orientation22. The angular distance of crystallographic c-axes in adjacent nanocrystals can vary by tens of degrees, and their orientation gradually changes within and across each rod by as much as 30–90° (ref. 22). Hereafter, we term this non-zero angular distance between the c-axes of adjacent nanocrystals simply ‘misorientation’. Molecular dynamics simulations have shown that misorientation deflects cracks and therefore toughens tooth enamel22. 1 Department of Physics, University of Wisconsin, Madison, WI, USA. 2Departments of Chemistry, Materials Science, Geoscience, University of Wisconsin, Madison, WI, USA. 3Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. 4Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA. 5School of Natural Sciences, University of Kent, Canterbury, UK. 6Department of Anthropology, Ohio State University, Columbus, OH, USA. 7Department of Earth Sciences, National Museum of Kenya, Nairobi, Kenya. 8UMR 7206 Eco-anthropology, Musée de l’Homme, MNHN, CNRS, UParis Cité, Paris, France. 9Oral Health, UMR_S 1333, UParis Cité, Montrouge, France. 10Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. 11Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. 12Earth and Planetary Science Department, University of California Berkeley, Berkeley, CA, USA. 13School of Anthropology and Conservation, University of Kent, Canterbury, UK. 14Present address: Department of Biology, Ball State University, Muncie, IN, USA. ✉e-mail: ; 76 | Nature | Vol 654 | 4 June 2026 Misorientation 10 nm Enamel thickness 1 mm 1 mm Caries rate Dental wear 1 mm Tooth size 1 cm Jaw robustness Older than 2.8 Ma Hominins before Homo 2,000,000–1,500,000 years BP Early Homo, transition to meat 12,000–5,000 years BP Transition to agriculture Present 10 BP 100 BP 1 ka 10 ka 100 ka 1 Ma 10 Ma 10 cm 250–100 years BP Industrial Revolution Present Fig. 1 | Hominin dentitions have changed in relation to dietary changes over the past 10 million years. Since hominins diverged from the last common ancestor shared with chimpanzees, significant dental changes occurred over the millimetre-to-centimetre scales. Compared with the earliest hominins, modern humans have less robust jaws, smaller posterior teeth and thinner enamel, as well as less occlusal wear but greater caries prevalence (10 cm−1 mm, previous work; all references and details are presented in Supplementary Tables 3–8). At the nanoscale (10 nm), modern humans have more misoriented enamel than the earliest hominins, as reported here in magenta (this work). The enamel formation mechanism, comprising organic matrix deposition, amyloid-like nanoribbons23, subsequent mineralization and resorption of the organic matrix, is conserved across all mammals, including primates24. Although primates differ in size (teeth, mouths, bodies, brains) and developmental rates25, they do not differ in enamel rod size, the presence of decussation patterns or nanocrystal sizes26. Thus, it is possible to make controlled comparisons of adjacent enamel nanocrystals across spe (...truncated)