Enamel, the hardest tissue in vertebrates, is formed of tightly packed rods made up of tiny hydroxyapatite crystals, and interrods, the spaces between them.<\/p>\n
Pupa Gilbert<\/a>, a biophysicist at the University of Wisconsin\u2013Madison, has previously shown how misorientation of individual crystals in these rods correlates with hardness in tooth enamels<\/a>. She and colleagues have now explored how the nanoscale arrangement of these individual crystals changed in the teeth of humans and other primates over time.<\/p>\n To do this, the researchers compared premolar teeth in 12 species across different periods from fossil records and found that the orientations of the crystals, or the angles between adjacent ones, changed with increasing food hardness. In humans, there were two main changes: the first was about 1.5 million\u20132.0 million years ago, corresponding to the transition to meat eating, and the other about 12,000 years ago, when agriculture introduced stone-ground grains in the diet. In nonhuman primates and monkeys, those with diets consisting primarily of fruit have the least amount of misorientation, while species that consume seeds have the highest.<\/p>\n The enamel crystal nanostructure from six species, as human diet\u2019s changed, so too did the nanostructure of our tooth enamel.<\/p>\n Credit: The researchers also found that a third major dietary shift that took place during the Industrial Revolution didn\u2019t correspond with any nanolevel alteration in enamel structure. Mackie O\u2019Hara<\/a>, a coauthor of the new paper and an anthropologist at Ball State University, says one possible reason is that the Industrial Revolution is quite recent\u2014\u201conly about 200 years old.\u201d With evolution in general, just because something can evolve doesn\u2019t mean that it has to, she says. \u201cEspecially in the case of enamel, there are so many different hierarchical levels of the structure that any one of those levels could be affected due to any environmental condition.\u201d<\/p>\n The researchers say their findings on the crystal misorientation in enamel\u2019s nanostructure could be of interest to materials scientists developing bioinspired materials.<\/p>\n![\"The](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/06\/493000-crystalnanostructure.webp\")
\n The enamel crystal nanostructure from six species within stylized drawings of each species\u2019 molar.<\/p>\n
\n Emma Lagan and Pupa Gilbert<\/p>\n