The study by Oliva et al. investigates the factors that predict zoonotic spillover from mammals to humans. The authors analyze a comprehensive database of 2,805 mammal-virus associations, covering 754 mammal species and 586 unique viral species. They find that both the total number of viruses infecting a species and the proportion likely to be zoonotic are predictable. Key factors influencing viral richness and zoonotic potential include phylogenetic relatedness to humans, host taxonomy, and human population within a species range. Bats are identified as harboring a significantly higher proportion of zoonotic viruses compared to other mammalian orders. The study also identifies regions with the highest number of 'missing viruses' and 'missing zoonoses,' highlighting areas of high value for future surveillance. Additionally, the authors develop a framework to assess the zoonotic potential of newly discovered mammalian viruses based on viral traits such as phylogenetic host breadth and viral replication properties. The findings provide a novel approach to understanding and predicting zoonotic spillover, which is crucial for pandemic surveillance and public health.The study by Oliva et al. investigates the factors that predict zoonotic spillover from mammals to humans. The authors analyze a comprehensive database of 2,805 mammal-virus associations, covering 754 mammal species and 586 unique viral species. They find that both the total number of viruses infecting a species and the proportion likely to be zoonotic are predictable. Key factors influencing viral richness and zoonotic potential include phylogenetic relatedness to humans, host taxonomy, and human population within a species range. Bats are identified as harboring a significantly higher proportion of zoonotic viruses compared to other mammalian orders. The study also identifies regions with the highest number of 'missing viruses' and 'missing zoonoses,' highlighting areas of high value for future surveillance. Additionally, the authors develop a framework to assess the zoonotic potential of newly discovered mammalian viruses based on viral traits such as phylogenetic host breadth and viral replication properties. The findings provide a novel approach to understanding and predicting zoonotic spillover, which is crucial for pandemic surveillance and public health.