*The decline of mammal functional and evolutionary diversity worldwideJedediah F. Brodie, Sara Williams & and Brittany GarnerPNASJanuary 19, 2021 Significance* The ongoing loss of species around the world is reducing the diversity of ecological roles played by organisms in natural communities, as well as the number of evolutionary lineages that live there. We have limited knowledge about which anthropogenic threats have the strongest influence on functional and evolutionary diversity, and about whether declines in these facets of biodiversity are faster or slower than the corresponding declines in species numbers. Here we show that harvest and habitat loss in the most biodiverse parts of the world disproportionately affect mammal species that have unique roles in their ecosystems. Enhanced conservation, focused particularly on harvest sustainability, is critically needed to avoid deterioration of ecosystem function and impoverishment of our biodiversity heritage. *Abstract* Biodiversity is declining worldwide. Because species interact with one another and with their environment, losses of particular organisms alter the function of ecosystems. Our understanding of the global rates and specific causes of functional decline remains limited, however. Species losses also reduce the cumulative amount of extant evolutionary history (“phylogenetic diversity” [PD]) in communities—our biodiversity heritage. Here we provide a global assessment of how each known anthropogenic threat is driving declines in functional diversity (FD) and PD, using terrestrial mammals as a case study. We find that habitat loss and harvest (e.g., legal hunting, poaching, snaring) are by far the biggest drivers of ongoing FD and PD loss. Declines in FD in high-biodiversity countries, particularly in Southeast Asia and South America, are greater than would be expected if species losses were random with respect to ecological function. Among functional guilds, herbivores are disproportionately likely to be declining from harvest, with important implications for plant communities and nutrient cycling. Frugivores are particularly likely to be declining from both harvest and habitat loss, with potential ramifications for seed dispersal and even forest carbon storage. Globally, phylogenetically unique species do not have an elevated risk of decline, but in areas such as Australia and parts of Southeast Asia, both habitat loss and harvest are biased toward phylogenetically unique species. Enhanced conservation efforts, including a renewed focus on harvest sustainability, are urgently needed to prevent the deterioration of ecosystem function, especially in the South American and equatorial Asian tropics. *ABSTRACT LINK* https://www.pnas.org/content/118/3/e1921849118