Scientists have uncovered how narwhals grow their unique, straight tusks, a discovery that sheds light on the structure of these unusual teeth but leaves their exact purpose in question. Narwhals are known for their long, straight tusks—actually a single, modified tooth—reaching up to three meters (10 feet) in length. These tusks were once mistaken for magical unicorn horns during the Middle Ages. In male narwhals, the left canine tooth grows through the jaw and upper lip to form the tusk, while the right canine remains inside the skull. To solve the "narwhal tusk puzzle," a team of biologists, chemists, and physicists used advanced 3D X-ray technology, including scans from three European particle accelerators known as synchrotrons. These scans revealed that the tusks are composed of two types of dental tissue: dentin on the inside and cementum on the outside. At a molecular level, the inner dentin forms a right-handed spiral, while the outer cementum forms a left-handed spiral. These opposing spirals create the straight structure of the tusk, unlike the curved tusks of other animals like elephants. The researchers were also surprised to find growth layers inside the tusks, similar to the rings in a tree, which can provide clues about the narwhal’s life history. Since narwhals can live up to 80 years, these layers may reveal details about their growth, health, and environment over time. The study used tusks from museums and those collected by Greenland's Indigenous Inuit people, who have traditionally hunted narwhals for food and cultural reasons. The exact purpose of the tusk remains a topic of debate among scientists. Some suggest it may be used for dominance displays or to attract mates, as observed in a tusk-measuring contest between two male narwhals in the presence of a female. However, others, like Martin Nweeia, a Harvard University dental anthropologist not involved in the study, argue that the tusk functions primarily as a sensory organ, based on his previous research. Despite the disagreement, Nweeia praised the study for its contribution to understanding the tusk’s detailed structure and form.