Comparison of 27 high-altitude mammal species with their low-altitude relatives found that the high-altitude species had fewer genes for olfactory reception and smaller olfactory bulbs.
Summary: https://phys.org/news/2025-07-animals-higher-elevations-decreased.html
Original paper (not open access): https://www.cell.com/current-biology/abstract/S0960-9822(25)00677-3?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982225006773%3Fshowall%3Dtrue