Using ancient DNA provides unique insights into the evolutionary history of species, particularly those that have experienced extreme environmental conditions, such as the last glacial period. This project aims to use ancient DNA from Late Pleistocene bears (Ursus spp.) present in North America and Eurasia to study different evolutionary processes, including demographic history, population dynamics, and ancient hybridization. Brown bear populations have experienced multiple waves of migration and hybridization, resulting in variations in population dynamics and adaptations to an ever-changing environment. They have also survived the last glacial period, while other megafauna couldn’t, providing a broader model of megafaunal resistance to environmental changes. To address this, I will generate and analyze whole-genome sequencing data within a comparative framework that includes modern and ancient whole-genome sequences of brown and polar bears. I will use mitochondrial DNA to determine the matrilineal phylogenetic placement and nuclear genomic data to assess hybridization patterns. Genetic diversity and population structure will also be assessed relative to modern and ancient Eurasian and North American brown bear samples. Collectively, these results will contribute to a better understanding of megafaunal persistence during the last glacial period.